Evidence based medicine & Appraising methodology

Question 1

Define a case report study

Answer 1

Single person/case is studied

- Prone to chance & bias!

Question 2

Define a case series

Answer 2

Group of people are studied

- Good for rare diseases

Question 3

Define a cohort study

Answer 3

Group of subjects exposed to a risk factor are matched to group not exposed to the risk factor

Question 4

Are cohort studies good for rare diseases or rare exposures?

Answer 4

Rare exposures

Question 5

Give an example of a influential cohort study

Answer 5

Review of mortality of doctors in relation to their smoking habits - Doll & Bradford

Question 6

Define a case control study

Answer 6

Group of subjects with an outcome are matched to group who don’t have the outcome
- Used to investigate cause of the outcome

Question 7

What type of bias can case control studies be prone to?

Answer 7

Recall bias - also have to rely on records

Question 8

Give an example of an influential case control study

Answer 8

Smoking and carcinoma of the lung - Doll & Bradford

Question 9

Are case control studies good for rare diseases or rare exposures?

Answer 9

Rare diseases

Question 10

Define a nested case control study

Answer 10

Conducted on a population taking part in a cohort study once sufficient numbers of outcomes have been reached. The nested case control can investigate exposures no previously taken into consideration
- Cases in the study are matched to controls from the same cohort

Question 11

Define a case cohort study

Answer 11

Similar recruitment to case control study but the control group is recruited from everyone in the initial cohort regardless of their future disease status

Question 12

Name the 9 Bradford Hill criteria (helps decide if causative relationship exists)

Answer 12

Strength
Consistency
Specificity
Temporality
Biological gradient
Plausibility
Coherence
Experimental evidence
Analogy

Question 13

What is a crossover trial?

Answer 13

Type of RCT, subjects receive one treatment then switch to the other halfway through the study

• Good to rare diseases where lack of subjects would effect power of study
• Can have carry over effects from first intervention if wash out period is too short

Question 14

Define an N-1 trial

Answer 14

Single subject is studied and receives repeated courses of drug or alternative treatment in random order

Question 15

What is the CONSORT statement?

Answer 15

Set of recommendations to improve the quality of RCT reports

Question 16

What are cross sectional surveys good for?

Answer 16

Establishing prevalence and association

- NOT causality

Question 17

What is a disadvantage of a cross sectional survey?

Answer 17

Prone to recall bias
Require large numbers of subjects
Groups can be unequal, confounders can be asymmetrically distributed

Question 18

Define economic analysis

Answer 18

Type of study assessing the cost and/or utilities of an intervention

Question 19

Name the 5 common methods used to obtain a sample from a population

Answer 19

Random sampling
Systematic sampling
Stratified sampling
Cluster sampling
Convenience sampling (prone to bias!)

Question 20

Define systematic sampling

Answer 20

Every nth member of the target population is selected

- Quasi random sampling

Question 21

Define stratified sampling

Answer 21

Different populations are recruited from subgroups in the target population based on one or more characteristics

Question 22

What are the 5 categories of bias

Answer 22

Reporting
Selection
Performance
Observation
Attrition

Question 23

What are the examples of reporting bias?

Answer 23

Literature search bias

Foreign language exclusion

Question 24

What are the examples of selection bias?

Answer 24

Sampling bias (researcher) - e.g Berkson bias
Response bias (subjects)

Question 25

What are the examples of performance bias?

Answer 25

Instrument bias | Questionnaire bias

Question 26

What are the examples of observation bias?

Answer 26

Interviewer bias Recall bias Response bias Hawthorne effect

Question 27

Define a positive confounder

Answer 27

Results in an association between two variables that are not associated

Question 28

Define a negative confounder

Answer 28

Masks an association that is present

Question 29

What methods are available for controlling confounders at the time of designing a study?

Answer 29

Restriction (inclusion & exclusion criteria) Matching (subjects with confounders are allocated equally to different arms of the study) Randomisation

Question 30

What methods are available for controlling confounders at the time of analysing a study?

Answer 30

Stratification Standardisation Statistical adjustment using multivariate techniques

Question 31

Which statistical technique can achieve stratification during analysis?

Answer 31

Mantel-Haenszel (gives adjusted relative risks as a summary measure of the over risk)

Question 32

When would you use multiple linear regression?

Answer 32

To minimise the effect of cofounders when dependent variables are continuous in nature

Question 33

When would you use logistic regression?

Answer 33

To minimise the effect of cofounders when variables are binary

Question 34

What are the two types of randomisation methods?

Answer 34

Fixed (methods defined and set up before the start of the trial) Adaptive (randomised groups are adjusted as the study progresses to account for imbalances)

Question 35

What are the types of fixed randomisation?

Answer 35

Simple Block Stratified

Question 36

What is a type of adaptive randomisation?

Answer 36

Minimisation (allocation of each subject dependent on the characteristics of those already enrolled)

Question 37

What are the three main endpoints used in studies?

Answer 37

Clinical (measurement of direct clinical outcome) Surrogate (measurement of outcome used as substitute for clinically meaningful endpoint) Composite (Combines several measurements into a single endpoint)

Question 38

Define validity

Answer 38

Extent to which a test measures what it is supposed to measure

Question 39

Define reliability

Answer 39

How consistent a test is on repeated measurements

Question 40

What are the types of validity?

Answer 40

``` Face Content Criterion (concurrent & predictive) Construct (convergent & divergent) Incremental ```

Question 41

Define face validity

Answer 41

Extent to which the test measures what it is supposed to measure

Question 42

Define content validity

Answer 42

Extent to which the test measures variables that are related to the parameter which should be measured by the test

Question 43

Define concurrent validity

Answer 43

Subtype of criterion validity | The extent to which the test correlates with a measure that has been previously validated

Question 44

Define predictive validity

Answer 44

Subtype of criterion validity | The extent to which the test is able to predict something that it should theoretically be able to predict

Question 45

Define convergent validity

Answer 45

Subtype of construct validity | Extent to which the test is similar to other tests measuring the same construct

Question 46

Define divergent validity

Answer 46

Subtype of construct validity | Extent to which the test is not similar to other tests that are measuring different constructs

Question 47

Define incremental validity

Answer 47

Extent to which the test provides a significant improvement in addition to the use of another approach

Question 48

Define intrarater reliability

Answer 48

Level of agreement between assessments by one rater of the same material at two or more different times

Question 49

Define inter-rater reliability

Answer 49

Level of agreement between assessments made by two or more raters at the same time

Question 50

Define test-retest reliability

Answer 50

Level of agreement between the initial test results and the results of repeat measurements made at a later date

Question 51

What test can be used to assess internal consistency?

Answer 51

Crohnbach's alpha >5 = moderate agreement >8 = exce;;ent agreement

Question 52

What is continuous data?

Answer 52

Can take any value e.g height

Question 53

What is Cohen's Kappa

Answer 53

Assesses the level of agreement for data that falls into categories

Question 54

What is the Kappa statistic?

Answer 54

Measures the level of agreement between assessments made by two or more raters at the same time where responses can fall into categories (aka inter-rater reliability) - Can help decipher if agreement is by chance

Question 55

What does a Kappa statistic of 0 mean?

Answer 55

Agreement between raters is chance only

Question 56

What does a Kappa statistic of 1 mean?

Answer 56

Agreement between raters is perfect beyond chance