March 2023 – Student Nurse Life

Examination of the Cardiovascular System

In patient assessment, following the process of history-taking, we’ll be looking into performing a thorough examination of the cardiovascular system.

Examination of the Cardiovascular System Outline

general considerations
examining the hands
examining the radial pulse, rhythm & rate
measuring the blood pressure
examining the face
examining the neck
examining the chest wall
examining the bases of the lungs
examining the abdomen
examining the lower limbs

1. General Considerations

If you haven’t done so already, introduce yourself and shake hands with your patient
Note the patient’s age and general state
Ensure that the examination room is quiet enough to perform auscultation
The patient should be properly undressed for this examination
The patient should be positioned adequately i.e. reclining at 45° with the head resting comfortably on pillows

2. Examining the Hands

FINGER CLUBBING

caused by interstitial oedema and dilation of the arterioles and capillaries
assess for finger clubbing by checking for the loss of the normal angle between the nail and the nail bed, and fluctuation of the nail bed
advanced finger clubbing may be featured through swelling of the subcutaneous tissues over the base of the nail causing the overlying skin to become tense, shiny and red, increase in the curvature of the nail especially in its long axis, and swelling of the pulp of the finger
finger clubbing causes may include cardiac issues such as cyanotic heart disease (heart disease that is caused by lack of oxygen) and infective endocarditis (inflammation of the endocardium, the inner lining of the heart, as well as the valves that separate each of the four chambers within the heart), respiratory issues such as bronchial carcinoma (a malignant cancerous tumour of the bronchi and the lung tissue), lung abscess (a type of liquefactive necrosis of the lung tissue and formation of cavities containing necrotic debris or fluid caused by microbial infection), bronchiestasis (a long-term condition where the airways of the lungs become widened, leading to a build-up of excess mucus that can make the lungs more vulnerable to infection), empyema (pus-filled pockets that develop in the pleural space), and fibrosing alveolitis (a disease involving the gas-exchanging portions of the lungs), and gastrointestinal issues such as inflammatory bowel disease (a term for two conditions – Crohn’s disease and ulcerative colitis, that are characterized by chronic inflammation of the GI tract), and liver cirrhosis (scarring of the liver caused by continuous, long-term liver damage).

examination of the cardiovascular system — Finger Clubbing – Retrieved from https://en.wikipedia.org/wiki/Nail_clubbing on 21st March 2023

PERIPHERAL CYANOSIS

can be physiological eg. due to a surrounding cold environment, reduced cardiac output eg. shock causes central cyanosis
featured through bluish discolouration of the nail beds
usually starts showing when patient is at <85% SPO2

SPLINTER HAEMORRHAGES

featured as small dark subungual petechiae
may be symptoms of infective endocarditis (inflammation of the endocardium, the inner lining of the heart, as well as the valves that separate each of the four chambers within the heart) as well as trauma

TAR-STAINED FINGERS

caused by smoking – smoking accellerates build-up of atherosclerosis which leads to CVA and/or peripheral vascular disease and ischaemic heart disease. Complete occlusion by athersclerosis causes a Myocardial Infarction.

TEMPERATURE

warm hands signify vasodilation
cold hands signify vasoconstriction
note if hands are dry or moist
clammy hands may be a sign of anxiety or sympathetic activation

3. Examining the Radial Pulse, Rhythm & Rate

ASSESSING THE RADIAL PULSE

the radial pulse can be located just lateral to the flexor carpi radialis
assess the rhythm – sinus (normal – controlled by the sino-atrial node)? irregular (due to atrial or ventricular extrasystoles, atrial fibrillation or heart block)?
assess the rate – 60-100bpm at rest = normal; >100bpm = sinus tachycardia (due to fever, exercise, anxiety, heart failure); fast arrhythmias (due to atrial fibrillation, supraventricular tachycardia, or ventricular tachycardia); <60bpm = bradycardia (due to high vagal tone in athletes, sleep, or certain medication eg. beta blockers or calcium antagonists)
assess the condition of the vessel wall – if vessel wall feels stiff and tortuous, atherosclerosis is probably present

4. Measuring the Blood Pressure

TAKING THE PATIENT’S BLOOD PRESSURE

the patient should not eat, smoke, take caffeinated products, or perform vigorous exercise for 30 minutes prior to the examination
the room should be quiet and adequately prepared so that the patient is comfortable
the patient’s arm should be positioned in a way so that the antecubital fossa is level with the heart
the bladder of the cuff should be centered over the brachial artery about 2cm above the antecubital fossa; the bladder length should not be less than 80% of the patient’s arm circumference
patient’s arm should be slightly flexed at the elbow
palpate the radial pulse and inflate the cuff until the pulse cannot be palpated any more, take note of the number displayed and deflate the cuff
place the stethoscope over the brachial artery
inflate the cuff to 30mmHg over the estimated systolic pressure
release the pressure slowly at about 5mmHg/second
note the measurement where you start hearing the korotkoff sound as the systolic pressure
note the measurement where you stop hearing the korotkoff sound as the diastolic pressure
record the patient’s blood pressure as systolic over diastolic
retake blood pressure measurement by repeating the same process on the other arm if the patient is visiting for the first time; if there is a difference in blood pressure of more than 10mmHg in one arm, record the highest reading

Category	Systolic	Diastolic
Normal	<130	<85
High Normal	130-139	85-89
Mild Hypertension	140-159	90-99
Moderate Hypertension	160-179	100-109
Severe Hypertension	180-209	110-119
Crisis Hypertension	>210	>120

Blood Pressure Classification in Adults

ASSESSING THE PULSE PRESSURE

pulse pressure is the difference between the systolic and diastolic blood pressure
a normal value of the pulse pressure falls somewhere between 30-40mmHg
a narrow pulse pressure may be a sign of reduced cardiac output such as in a haemorrhagic shock, as well as in severe aortic stenosis (prevents aortic valves from opening and closing properly, leading to stress on the heart to work harder to pump blood to the rest of your body), constrictive pericarditis (a condition in which granulation tissue formation in the pericardium results in loss of pericardial elasticity leading to restriction in the ventricular filling), and pericardial effusions (acute or chronic accumulation of fluid within the pericardial space)
a wide pulse pressure may be a sign of increased cardiac output and low vascular resistance, common in aortic insufficiency (heart valve disease where the aortic valve no longer functions adequately to control the flow of blood from the left ventricle into the aorta), anaemia (a condition in which the number of red blood cells or the haemoglobin concentration within them is lower than normal), and thyrotoxicosis (a clinical state of inappropriately high levels of circulating thyroid hormones T3 and/or T4 in the body)

PULSUS PARADOXUS

pulsus paradoxus is the difference between where the Korotkoff sounds are first heard on expiration only and where they are heard on both inspiration and expiration is normally 10mmHg
pulsus paradoxus is present when the difference exceeds 10mmHg
pulsus paradoxus is associated with pericardial effusion (acute or chronic accumulation of fluid within the pericardial space) and severe acute asthma

5. Examining the Face

CENTRAL CYANOSIS

can be easily noted when looking at the patient’s tongue
happens when the oxygen saturation of arterial blood falls below 80-85%; central cyanosis indicates lack of oxygen in the brain
may be a sign of congenital heart disease (conditions present at birth which affect the structure of the heart and the way it works) or chronic obstructive airways disease or COPD

ANAEMIA

anaemia is characterised by a reduction of haemoglobin concentration in the blood, which usually are <13.5g/dl in adult males and <11.5g/dl in adult females
anaemia can be noticed as pallor of the mucous membranes eg. the conjunctival mucosa (happens when the haemoglobin level is <9-10g/dl

CORNEAL ARCUS

corneal arcus is characterised by a greyish line in the periphery of the cornea, concentric with the edge but separated from it by a clear zone, consisting of cholesterol crystals
corneal arcus is typically seen in the elderly, but when seen in young people, it may be a sign of hypercholesterolaemia

XANTHELASMA

xanthelasma is characterised by intracutaneous yellow cholesterol deposits around the eyes
xanthelasma can be noted in normal people as well as in those with hypercholesterolaemia

MALAR FLUSH

malar flush is characterised by redness of the cheeks
malar flush is commonly seen in patients with mitral stenosis (narrowing of the valve between the two left heart chambers) as well as in normal individuals

6. Examining the Neck

JUGULAR VENOUS PRESSURE (JVP)

the jugular veins, which are located adjacent to the superior vena cava, directly reflect right arterial pressure
assessing the right internal jugular vein is better since it is more proximal to the superior vena cava than the left; the right external jugular vein has venous valves between it and the superior vena cava, hence it is less preferred for assessment; ideal patient placement is at 45 degree angle, looking to his left
jugular venous pressure (JVP) can be noted as a double flicker above the clavicle parallel to the anterior border of the sternocleidomastoid muscle (remember that a venous pulse is never palpable)
note the height by measuring the vertical height in cm between the top of the jugular venous pulsation and the sternal angle
normal JVP height = <4cm
high JVP height is a sign of increased pressure in the right atrium, and so, may be a sign of congestive heart failure, fluid overload (which may be due to nephrotic syndrome) or superior vena cava obstruction
note the waveform: a wave signifies right atrial systole whilst an absent waveform may be due to atrial fibrillation; c wave, which is rarely noted, is due to tricuspid valve closure; x descent (systolic collapse) is a sign of atrial relaxation and downward displacement of the tricuspid valve towards the right ventricular apex in ventricular systole; v wave is due to right atrial filling; y descent (diastolic collapse) is a sign of a fall in right atrial pressure when the tricuspid valve opens
giant a waves happen when the right atrium is contracting against resistance as in tricuspid stenosis; cannon a waves happen when the right atrium is contracting against a closed tricuspid valve as in complete heart block
the hepatojugular reflux helps in re-checking an already raised jugular venous pressure; it is done by pressing with the flat of the hand over the liver and watching the rise of the JVP

Jugular Venous Pulse – Retrieved from https://sketchymedicine.com/2015/05/jugular-venous-pulse-jvp/ on 24th March 2023

THE CAROTID PULSE

the carotid pulse is the closest point to the heart where the arterial pulse can easily be felt
note the waveform of the pulse: slow rising pulse = moderate to severe aortic stenosis; collapsing pulse = aortic incompetence; double peak pulse a.k.a bisferiens = moderate aortic stenosis with severe incompetence
assess the pulse volume: small volume = low cardiac output; large volume = anaemia or thyrotoxicosis

Carotid Pulse – Retrieved from https://3d4medical.com/blog/the-anatomy-behind-pulse-points on 24th March 2023

7. Examining the Chest Wall

SCARS FROM PAST SURGERIES

left infra-mammary scar is a sign of past closed mitral valvotomy
central sternal scar is a sign of past open heart surgery

APEX BEAT

determine the position of the apex beat, which is the lowest and outermost point of definite cardiac pulsation; the apex is usually found in the 5th intercostal space within the mid-clavicular line
the apex beat may be impalpable in individuals with COPD and in patients with obesity
the apex may be displaced due to ventricular enlargement following cardiac failure, pneumothorax and scoliosis
assess the quality of the cardiac impulse: normal = brief outward movement at the onset of left ventricular ejection; abnormal = thrusting displaced apex beat in volume overload due to active large stroke volume ventricle caused by mitral or aortic incompetence, sustained apex beat in pressure overload due to aortic stenosis and gross hypertension with a normal or reduced stroke volume; or parasternal heave in central thrust or lift in the sternal region or 3rd or 4th intercostal space indicating right ventricular hypertrophy
assess for palpable murmurs a.k.a. thrills or palpable heart sounds at the apex and base of heart; systolic thrill at apex = due to a ventricular septal defect or mitral regurgitation; systolic thrill at base = due to aortic or pulmonary stenosis; diastolic thrill at the apex = mitral stenosis; diastolic thrill at the base = aortic regurgitation; palpable first heart sound (sounds like a tapping apex beat) = felt in mitral stenosis; palpable pulmonary sound = felt in pulmonary hypertension

PRAECORDIUM AUSCULTATION

prior to auscultation of the parecordium, ensure surrounding area is quiet
use the diaphragm of the stethoscope to filter out low pitched sounds and identify high pitched sounds eg. 2nd heart sound
use the bell of the stethoscope to listen to low-pitched sounds eg. mitral stenosis murmur
aortic valve = best heard at the right 2nd intercostal space close to the sternum; pulmonary valve = best heard at the left 2nd intercostal space close to the sternum; tricuspid valve = best heard at the left 3rd, 4th and 5th intercostal spaces close to the sternum; mitral valve = best heard at the apex
heart sound S1 = closing mitral and tricuspid valves + upstroke of carotid pulse; loud S1 = mitral stenosis; faint S1 = mitral regurgitation; intensity variation = atrial fibrillation
heart sound S2: loud S2 = systemic or pulmonary hypertension; soft S2 = calcified or immobile aortic or pulmonary valve; fixed splitting S2 = atrial septal defect; reversed splitting S2 on expiration = delayed aortic component follows pulmonary component; fixed splitting S2 on inspiration = aortic component superimposed on the normal pulmonary component, usually in left bundle branch block (delay in the activation of left ventricle)
extra heart sounds: S3 = low-pitched sound following S2 which happens in rapid ventricular filling in early diastole (physiologically heard in children, healthy young adults, athletes, and in pregnancy; pathologically heard in patients with large poorly contracting ventricle or with increased ventricular stroke volume due to a leaking heart valve)
extra heart sound: S4 = soft low-pitched sound occurring just before S1 in rapid emptying of a hypertrophied atrium, always abnormal, commonly associated with severe heart failure and/or hypertension

AUSCULTATING FOR MURMURS

heart murmurs are music-like sounds caused by turbulent blood flow in the heart; murmurs can result from normal blood volume passing through an abnormal valve, or from increased blood volume passing through a normal valve
assess murmur timing – is it systolic or diastolic? (you may compare with the carotid pulse, and if murmur accompanies the pulse would be systolic, while if it follows the pulse it would be diastolic)
ejection systolic murmurs start after the 1st heart sound, increase in amplitude to a peak around mid-systole, and quiet down towards the end of systole, stopping completely before the 2nd heart sound; causes include aortic stenosis, pulmonary stenosis (normal volume of blood flowing through a narrowed valve), and pregnancy (due to increased blood volume flowing through a normal valve)
pansystolic murmurs extend throughout systole to the 2nd heart sound; causes include mitral or tricuspid valve leakage, or a ventricular septal defect
late systolic murmurs are variants of the pansystolic murmurs, but these do not start right after the first heart sound but later on in systole; common in mitral valve prolapse
early diastolic murmurs start right after the 2nd heart sound and quiet down as diastole proceeds; causes include aortic and/or pulmonary regurgitation
mid-diastolic murmurs are low-pitched rumbling sounds best heard with the stethoscope bell at the apex of the heart while the patient is rolled onto the left hand side; occurs in mitral stenosis and rarely in tricuspid stenosis
continuous murmurs are heard during systole and diastole; occur in patients with ductus arteriosus (channel connecting the aorta and pulmonary artery, which normally closes after birth)
assess murmur intensity – murmur intensity is measured by grades…Grade 1 = heard by an expert in optimum conditions; Grade 2 = heard by a non-expert in optimum conditions; Grade 3 = easily heard, no thrill; Grade 4 = loud murmur with a thrill; Grade 5 = very loud, commonly heard over a wide area, with a thrill; Grade 6 = extremely loud, heard without a stethoscope
assess murmur site and radiation – aortic stenosis = to the upper right sternal edge and neck; aortic rugurgitation = down the left sternal border and towards the apex; mitral stenosis = localised to the apex; pulmonary stenosis = to the upper left sternal border and beneath the left clavicle; pulmonary regurgitation = down the left sternal border; tricuspid stenosis = localised to the lower left sternal border; tricuspid regurgitation = lower left and right sternal border and epigastrium; ventricular septal defect = lower sternal edge
assess murmur pitch – high pitch = greater pressure gradient; aortic incompetence murmur is high pitched so it is best heard with the diaphragm of the stethoscope; mitral stenosis murmur is low pitched so it is best heard with the bell of the stethoscope

AUSCULTATING FOR ADDED SOUNDS

ejection click = opening sound caused by thickened aortic and pulmonary valves; happen right after first heart sound and before any ejection murmur
prosthetic heart valves = usually have a quiet opening sound and a louder closing sound, seemingly metallic in character
pericardial rub = friction sound common in acute pericarditis, usually heard by the diaphragm of the stethoscope left of the lower sternum with the patient breathing out, with intensity varying from hour to hour and with patient positioning

8. Examining the Bases of the Lungs

crackes indicate pulmonary oedema, since they are produced by the explosive re-opening of collapsed airways

9. Examining the Abdomen

palpate for the liver – enlarged liver is a sign of right heart failure; enlarged and pulsatile liver is a sign of tricuspid regurgitation
palpate for aortic aneurysm – felt as a pulsatile mass over the epigastrium; a bruit may also be heard over it

10. Examining the Lower Limbs

PALPATE FOR THE PERIPHERAL PULSES

femoral pulse = midway between the symphysis pubis and the anterior superior iliac spine
popliteal pulse = deep in the popliteal fossa
dorsalis pedis artery = along the cleft between the first two metatarsals
posterior tibial artery = half-way along a line between the medial malleolus and the prominence of the heel
NOTES: always compare left and right sides; always listen for bruits at all sites on both sides (heard over narrowed arteries); if peripheral pulses are impalpable, the problem may be peripheral vascular disease

Peripheral Pulses – Retrieved from https://www.brainkart.com/article/Assessment-of-Vascular-Disorders–Health-History-and-Clinical-Manifestations_31948/ on 30th March 2023

ASSESS FOR SACRAL & LOWER LIMB OEDEMA

oedema is the result of increased interstitial fluid that causes swelling of the tissues
subcutaneous oedema can be determined by pitting of the skin following firm pressure applied by a finger or a thumb for a few seconds

Examination of the Cardiovascular System

Summary

Step-by-step instructions on how to perform an examination of the cardiovascular system:

assess hands for finger clubbing, peripheral cyanosis, tar staining
assess face for yellow lesions close to the inner eyes, malar flush, central cyanosis
assess neck: palpate the carotid artery & determine pulse rate, rhythm and volume; calculate CVP
assess chest: determine apex beat placement
auscultate for heart sounds and murmurs
check pedal pulses and for pitting oedema

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Introduction to Patient Assessment and Implementation of Care

Patient assessment and implementation of care requires a systematic history-taking approach, which has to be professional yet able to gain the patient’s confidence and trust. Acquired patient history should include all information relevant to the illness in question, as well as general information about the patient and his or her background, social situation and other problems. Patient assessment should be carried out in a holistic way.

History-Taking Basic Principles

Ensure that the interview with the patient is taking place in an appropriate, comfortable and private setting
Introduce yourself and shake hands with the patient
Address and remember the patient with his or her name
Treat with respect and courtesy

Basic History-Taking Outline

presenting complaint history
medical & surgical history
drug history
family history
social history
systematic enquiry

1. Presenting Complaint History

Acquire basic information such as client’s full name, age and address
Establish the nature and duration of the presenting complaint – when did it start? how? try to acquire the chronological order of main symptom/s onset
Obtain duration, onset (was it sudden or gradual?), continuation (constant or periodic? frequency? improving or progressing?), precipitating or relieving factors, and associated symptoms eg. feeling lightheaded, out of breath, or sweaty
If pain is a symptom, determine site, radiation, character (ache? pressure? shooting pain? stabbing pain? dull pain?) and severity (does it stop you from functioning as normal? does the pain wake you up from your sleep?); pain originating from organs is usually dull and compressive, while pain originating from the surface is usually sharp

2. Medical & Surgical History

Previous illnesses
Previous admissions to hospital
Previous surgeries (keep in mind that recent surgery may lead to Pulmonary Embolism)
Other comorbidities eg. diabetes mellitus, hypertension, hyperlipidaemia, fits, CVAs, heart disease and psychiatric illness

3. Drug History

Obtain names of all medications that the patient is taking, including over-the-counter drugs, herbal medicines and laxatives
Determine each drug’s dose, administration frequency, and compliance
Ask about any known drug allergies or suspected reactions

4. Family History

Obtain information about any genetic diseases eg. beta thalassaemia
Obtain information about other diseases eg. hypertension and coronary artery disease which are influenced more with predisposed environmental factors eg. diet and smoking; in the case of heart disease ask about whether the patient’s parents, siblings or children have experienced heart disease

5. Social History

Ask about the patient’s home environment especially where the patient has mobility or cardio-respiratory problems; determine the number of people living together in the house, the number of rooms, any need for bathroom arrangements, heating (or lack of), steps leading to the house, steps inside the house, and the possibility of the patient sleeping on ground-floor level
Ask about the patient’s occupation, taking note of any possible exposure to substances related to the patient’s presenting symptoms; unemployment may be a predisposing factor for mental and physical problems; occupation history may provide an insight to the patient’s financial situation
Ask the patient about personal interests; lack of interests may lead to lack of lifestyle appreciation
Ask about any habits that may impact the patient’s health eg. alcohol abuse (including quantity of alcohol consumption per day or week – regular consumption of more than 21 units of alcohol per week in males or 14 units in females pose a significant risk of developing alcohol-related disorders such as liver cirrhosis and pancreatitis, as well as hypertension); if patient is a heavy drinker, determine consumption quantity, age of onset of drinking, amount of money spent on alcohol per week, previous drinking habits, related hospital admissions, time of a typical day’s first alochol consumption, and whether drinking happens mostly at home or in a particular place
Ask about smoking habits, and if present, determine how many cigarettes does the patient smoke daily, as well as age of onset of smoking
Ask about drug abuse, and if present, what type of drug is being used, mode of administration, any sharing of needles, status of hepatitis and HIV, age of onset of drug use, and reason for using drugs

6. Systematic Enquiry

Enquire about any other symptoms that may indicate any other unsuspected disease; the following checklist may help…

Cardiovascular Symptoms

– chest pain on exertion

– orthopnoea (breathlessness when lying flat)

– paroxysmal noctournal dyspnoea (nocturnal breathlessness attacks)

– palpitations

– ankle swelling

– pain in legs upon exertion

Respiratory Symptoms

– shortness of breath upon exertion

– wheezing

– coughing

– sputum (note colour and amount)

– haemoptysis (blood-stained sputum)

– chest pain in relation to respiration or coughing

Gastroenterological Symptoms

– mouth condition (check for tongue infection or bleeding gums)

– dysphagia (difficulty swallowing)

– indigestion

– heartburn

– abdominal pain

– weight loss

– change in bowel habits

– stool colour (pale, tarry black, bloody)

Urogenital Symptoms

– dysuria (pain on passing urine)

– urine-passing frequency during the day and night

– haematuria (blood in urine)

– number of sexual partners

CNS-Related Symptoms

– headaches

– fits

– parasthaesia (tingling)

– numbness

– muscle weakness

– hearing problems (eg. deafness, tinnitus)

– excessive thirst

– sleep patterns

Vision-Related Symptoms

– appearance of the eyes

– vision disturbance

– pain

Locomotor Symptoms

– joint pain or stiffness

– muscle pain or weakness

Endocrine System Symptoms

– heat or cold intolerance

– change in sweating

– prominence of the eyes

– swelling of the neck

Male-Related Symptoms

-prostatic symptoms (difficulty in starting/passing urine, poor stream, post-micturition dribbling)

– erections, ejaculation, frequency of intercourse, urethral discharge

Female-Related Symptoms

– pre-menopausal (age of onset of periods, regularity, length, blood loss, contraception, and vaginal discharge)

– post-menopausal bleeding

– stress and urge incontinence

– libido and pain during intercourse

Concluding the History

ask the patient whether he or she would like to add anything else
summarise information given and allow the patient to correct you if or where you are wrong
by analysing the collected information, you may now be able to reach a provisional diagnosis and emphasise on the related physical examination components for patient assessment continuation.

NOTE: when starting a patient assessment, while gathering the patient’s history, it is important to use selective questions to clarify information being relayed, however, do not suggest symptoms or answers to the patient, as that may lead to inaccurate information.

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Statistical Correlation Tests, Bias, Risk & More

Statistical Correlation Tests

Statistical correlation tests are performed with the aim of finding out whether a relationship exists between variables, and then determining the magnitude and action of that relationship. In other words, correlation is a statistical measure that expresses the extent to which two variables are linearly related. It’s commonly used for describing simple relationships without making a statement about cause and effect.

If two variables tend to move up or down together, they are considered to be positively correlated. However, if they tend to move in opposite directions, they are considered to be negatively correlated.

Parametric tests are based on an assumption that the data being analyzed follows a normal distribution. The more data points a distribution has, the more it can approach a normal distribution. Lack of data points would require the use of non-parametric tests.

Non-parametric tests a.k.a. distribution-free tests are methods of statistical analysis that do not require a distribution to meet the required assumptions to be analyzed, especially if the data is not normally distributed.

Student T-Test

statistical correlation tests — Retrieved from https://researchbasics.education.uconn.edu/t-test/ on 11th March 2023

UNPAIRED T-TEST – testing two means

The unpaired t-test a.k.a. independent t-test is a statistical test which aims to determine whether there is a difference between two unrelated groups. The unpaired t-test is used to make a statement about the population based on two independent samples. To make this statement, the mean value of the two samples is compared.

ANOVA – testing more than two means

ANOVA a.k.a. Analysis of Variance, is a statistical test used to investigate the difference between the means of more than two groups. A one-way ANOVA uses one independent variable, whereas a two-way ANOVA uses two independent variables.

CHI-SQUARED TEST – testing the association between two categorical variables

A chi-squared test is a statistical test that is used to compare observed and expected results. The main aim of the chi-squared test is to identify whether a disparity between actual and predicted data is due to chance or to a link between the variables under consideration.

Choosing the Right Test

Bias Potential Sources

Bias is the systematic deviation from the truth. Different sources of bias may include:

selection or sampling bias – inadequate selection of study participants usually due to high non-response rate, inadequate follow-up, inadequate sampling method use, or inadequate controls or comparisons groups
confounding bias – existing differences between comparison groups in one or more parameters which may be directly associated with the outcome and the candidate risk factor in question
instrumental bias – faulty measurement instrumentation due to lack of calibration, inaccurate diagnostic tests, etc
information bias – systematically incorrect measurements or responses, or from differential misclassification of disease or exposure status of participants eg. due to questionnaire ambiguity or insensitivity
systematic bias – one observer may underestimate readings, leading to his respondents having lower readings than those observed by someone else
respondent bias – misunderstandings, lack of interest, or recall issues in the unaffected group
random bias – observer may underestimate or overestimate measurements, which mistakes tend to even out on averaging

Calculating Statistical Risk

In statistics, the risk for a particular group to develop a disease refers to the rate of disease in the group concerned.

RISK DIFFERENCE / ABSOLUTE RISK – the excess risk that exposed individuals have.

RISK RATIO – the measurement of the risk in the exposed group as a multiple of the risk in the unexposed group.

ODDS RATIO – odds refer to the chance of developing the disease rather than not developing the disease. Odds Ratio refers to the chances of developing the condition for an exposed individual relative to an unexposed individual.

The Relevance of Testing the Sensitivity & Specificity of a Screening Diagnostic Test

Screening programs need to provide diagnostic tests with the least disturbance possible for the individual, yet with enough sensitivity and specificity to detect the disease in question. Assessing the sensitivity and specificity of a test requires its outcome to be compared against a gold standard eg. comparing the Faecal Occult Blood Test sensitivity and specificity to a colonoscopy, in this case considered to be the gold standard.

Multi-Variate Analysis

Linear regression analysis is used to predict the value of a variable based on the value of another variable. The variable you want to predict is called the dependent variable, while the variable you are using to predict the other variable’s value is called the independent variable.

Logistic regression is a statistical analysis method to predict a binary outcome eg. yes or no, based on prior observations of a data set. A logistic regression model predicts a dependent data variable by analyzing the relationship between one or more existing independent variables. This technique results in an odds ratio rather than a rate of change per unit change in the independent variable.

Poisson Regression models are best used for modeling events where the outcomes are counts. Or, more specifically, count data: discrete data with non-negative integer values that count something, like the number of times an event occurs during a given time-frame or the number of people in line at the grocery store. This technique results in a risk ratio instead of a rate of change per unit change in the independent variable.

Example of Poisson Regression – Retrieved from https://sherrytowers.com/2018/03/06/poisson-regression/ on 15th March 2023

Survival Analysis is concerned with studying the time between entry to a study and a subsequent event. Originally the analysis was concerned with time from treatment until death, hence the name, but survival analysis is applicable to many areas as well as mortality.

Example of Survival Analysis – Retrieved from https://www.graphpad.com/guides/survival-analysis on 15th March 2023

Relative Survival is defined as the ratio of the proportion of observed survivors in a cohort of cancer patients to the proportion of expected survivors in a comparable set of cancer free individuals. The formulation is based on the assumption of independent competing causes of death.

Example of Relative Survival Analysis – Retrieved from https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0202044 on 15th March 2023

Meta-analysis is a research process used to systematically synthesise or merge the findings of single, independent studies, using statistical methods to calculate an overall or ‘absolute’ effect. Meta-analysis does not simply pool data from smaller studies to achieve a larger sample size.

Example of Meta-Analysis – Retrieved from https://www.mdpi.com/2624-8611/4/4/49 on 15th March 2023

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Statistical Considerations Central Tendency Null Hypothesis & More

Statistical considerations for research should include careful statistical planning and use of the right statistical tests for data analysis to ensure a successful research project.

Central Tendency – Mean, Median & Mode

Central Tendency

The phrase ‘Central Tendency’ refers to a single value which aims to describe a set of data through the identification of the central position within the same set of data. The mean, which at times is referred to as the average, is most commonly considered to be the measure of central tendency, however, there are also the median and the mode which can be considered as measures of central tendency. Which measure is valid depends on the conditions under which they are being evaluated.

medical statistics — Retrieved from https://danielmiessler.com/blog/difference-median-mean/ on 23rd November 2022

The Mean

The mean is the average, where all values are added together and then divided by the number of values.

The Median

The median is the middle value found within the list of values. To find the median you need to list all values in numerical order from smallest to largest, and then identify the value within the middle.

The Mode

The mode is the value occurring most often. This means that if in a particular list of values no number is repeated, there would be no mode for that particular list.

The Variance & Standard Deviation

The variance is a calculation of the normal distribution spread in a set of variables, in other words, a measure of dispersion. The standard deviation is the square root of its variance.

Hypothesis Testing Statistical Considerations

Define the Null Hypothesis – no difference between the groups being compared
Define an Alternative Hypothesis – existing difference between the groups being compared; defined difference should be clinically significant
Calculate a p value – the probability of obtaining the results observed if the null hypothesis is true
Based on the p value, accept or reject the Null Hypothesis
If the Null Hypothesis is rejected, accept the Alternative Hypothesis

NOTE: the size of an expected difference (priori) should be defined prior to the data collection period.

The Null Hypothesis

Studies always start out with the assumption that the difference between the groups being compared will be non-existent a.k.a. null, hence why this is called the Null Hypothesis. Studies aim to have enough evidence to accept or reject this null hypothesis.

Unfortunately, errors may be made in accepting or rejecting the null hypothesis. To prevent such errors, the researcher should aim to have a sample size which is large enough.

The Confidence Interval & P-Value

The phrase confidence interval refers to the range of values which a specific statistic, most commonly being a mean or proportion of the population, can have in the reference population with a specific probability. Confidence intervals help in clinical trial data interpretation by determining upper and lower bounds on the likely size of any true effect.

The p-value determines whether trial results could have occurred by chance.

Confidence intervals are usually preferred to p-values since they provide a range of possible effect sizes in relation to the data, whilst p-values provide a cut-off beyond which we assert that the findings are statistically significant.

A confidence interval which embraces the value of no difference between treatments shows that treatment being investigated is not significantly different from the control.

The cut-off point for rejecting the null hypothesis is arbitrary, a typically being equivalent to 0.05

If p = 0.01, the chance of obtaining the same results as the experiment is 1%, meaning that it is very unlikely, thus we reject the null hypothesis.

If p = 0.7, then the chance of obtaining the same results as the experiment is 70%, thus, we accept the null hypothesis.

NOTE: bias must be assessed before confidence intervals are interpreted, since biased studies can be misleading even when very large samples and very narrow confidence intervals were involved.

(Davies and Crombie, 2003)

Errors & Power Statistical Considerations

Type 1 (Alpha) & Type 2 (Beta) Errors in Statistics

Power statistical considerations

Power is determined by sample size, magnitude of difference sought, and by the arbitrary. For example, a pilot study with a small sample size would have low power. Power desired is usually 0.80

Reference

Davies, H.T.O. & Crombie, I.K. (2003). What are confidence intervals and p-values? What is…? Series. Edition 2009. Hayward Communications Ltd. Hayward Group Ltd. Retrieved from http://www.bandolier.org.uk/painres/download/whatis/What_are_Conf_Inter.pdf on 12th February 2023

Kirkwood, Betty R. (2003). essential medical statistics. Blackwell Science, Inc., 350 Main Street, Malden, Massachusetts 02148–5020, USA: Blackwell. ISBN978-0-86542-871-3.

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Case Control Studies Critical Appraisal

Case Control Studies are typically observational studies commonly used to outline factors related with certain diseases or outcomes. Selection of participants is done on the basis of an experienced outcome. However, to introduce the control aspect within the study, other participants are selected at random from the population without having experienced that outcome. In both the cases and controls participants, exposure is assessed retrospectively through medical records and interviews.

Retrieved from https://www.pinterest.com/pin/408912841140782725/ on 26th February 2023

Hierarchy of Evidence

Case Control Studies Participant Selection Criteria

CASES

clear inclusion/exclusion criteria to ensure homogeneity
cases should ideally be representative of the cases within the target population for external validity purposes
cases should be sourced from the community, clinic, or hospital
accurate diagnosis is important so as not to dilute the cases group with those who do not actually have the disease in question

CONTROLS

controls should be selected from the same population, and may include individuals at risk of developing the outcome
same inclusion/exclusion criteria but without the outcome should be used, with the emphasis being on comparability of cases and controls
accurate classification of controls should be ensured; if confounders are known, they should be matched through a matched study, otherwise, confounders need to be considered in data analysis, and a bigger sample would be required

Matching

Matching is an attempt to ensure comparability between the cases and controls. Matching reduces variability and systematic differences caused by extraneous variables a.k.a. confounders (such as age, gender and race), which may be related to the risk factor.

Bias

INTERVIEWER BIAS – interviewer asks the leading questions, which are different from those used for the control group.

DATA QUALITY – incomplete or inaccurate data

RECALL BIAS – Participants with the disease (CASES) are more likely to recall and report exposure due to having experienced the outcome

Advantages VS Disadvantages

ADVANTAGES	DISADVANTAGES
ideal when seeking possible causes of rare outcomes and outcomes with long latency	may be difficult to select appropriate controls group
does not require a large group of participants	extraneous variables a.k.a. confounder control may be incomplete
relatively quick since the outcome would have already occurred	difficult to validate information
multiple exposures or risk factors can be examined	susceptible to recall bias
relatively inexpensive

Performing Case-Control Studies

cases are identified
control group individuals with similar characteristics but without the outcome in question are identified
exposure is measured retrospectively in both groups
occurrence rate of exposure in cases is compared to the occurrence rate of exposure in control
results are typically obtained through odds ratios or relative risk: show occurrence in exposed is divided by occurrence in non-exposed; if value is 1 = no difference; if value is >1 = risk is higher in exposed; if value is <1 = risk is higher in non=exposed

Cohort Study VS Case Control Study

Retrieved from https://twitter.com/medicine20102/status/682169574859620352 on 26th February 2023

CASP Tool for Case Control Studies

CASP Tool for case-control studies can be accessed here.

To view blogpost featuring Cochrane videos on all types of studies please click here.

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Cohort Studies Critical Appraisal

Cohort Studies are observational studies on groups of people with defined characteristics in which outcomes related to particular exposure (or lack thereof) are compared. Cohort Studies are usually indicated in studies where manipulated exposure is considered to be unethical (eg. no group of people should be asked to smoke for the purpose of outcome comparison). Similarly, these are observational studies, thus they lack the opportunity to control or prevent the expected outcome.

Hierarchy of Evidence

Cohort Studies Advantages & Disadvantages

Cohort Studies need to include a control group – a group which is not exposed to the risk factor of interest. Participants are selected based on their exposure status at the start of the study, and exposed and unexposed groups need to be selected from the same population.

Advantages

exposure to the risk factor of interest is measured prior to disease onset, which reduced bias
rare exposures can be examined by appropriate selection of study cohorts
multiple outcomes can be studied for a single type of exposure
calculates incidence and relative risk of disease in both exposed and unexposed participants over time

Disadvantages

changes in the participants’ exposure status and diagnostic criteria that may happen over time can affect the individuals’ classification based on exposure and disease status; the researcher should think about what measures may need to be taken if the participants change their patterns throughout the study period
risk of information bias – outcome may be influenced by information on the participant’s exposure status
loss of follow-ups may introduce attrition bias, where the characteristics of drop-outs and those completing the study may be significantly different, leading to a reduction in the validity of the study
expensive and time consuming

Preventing Loss to Follow Up

During the recruitment process, the researcher should obtain all information required so that the participant can be easily contacted. In addition, the researcher should exclude participants that are likely to be lost (eg. a prospective participant may have plans to move to another country).

During the follow-up period, the researcher should maintain regular contact through different means, and possibly provide tokens or gifts to encourage continued participation.

Prospective VS Retrospective Cohort Studies

In Prospective Cohort Studies, participants are identified at the time of exposure. They are followed up over time until outcome occurs.

Advantages: Prospective Cohort Studies are designed with specific data collection methods.

Disadvantages: Such studies entail a long indefinite follow-up period until an outcome occurs. They are susceptible to loss of follow-up, and are usually expensive.

In Retrospective Cohort Studies, the chosen participants would have already been exposed to and subsequently experienced an outcome. Thus, outcome data measured in the past is then reconstructed for analysis.

Advantages: Retrospective Cohort Studies are cheaper and quicker than prospective studies, and make use of past data, which can be accessed immediately.

Disadvantages: Such studies are susceptible to both recall bias and information bias, and may be subjected to incomplete, inaccurate, or inconsistent data due to limited control over data collection.

Cohort Studies Critical Appraisal

Casp Tool

CASP Tool for Cohort Studies Critical Appraisal can be found here.

To view blogpost featuring Cochrane videos on all types of studies please click here.

Types of Statistical Tests Used in Cohort Studies

Risk Ratio (RR)
Odds Ratio (OR)
Confidence Interval (CI)

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