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Statistics! > Evidence based medicine & Appraising methodology > Flashcards

Evidence based medicine & Appraising methodology Flashcards

1
Q

Define a case report study

A

Single person/case is studied

- Prone to chance & bias!

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2
Q

Define a case series

A

Group of people are studied

- Good for rare diseases

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3
Q

Define a cohort study

A

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

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4
Q

Are cohort studies good for rare diseases or rare exposures?

A

Rare exposures

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5
Q

Give an example of a influential cohort study

A

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

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6
Q

Define a case control study

A

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

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7
Q

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

A

Recall bias - also have to rely on records

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8
Q

Give an example of an influential case control study

A

Smoking and carcinoma of the lung - Doll & Bradford

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9
Q

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

A

Rare diseases

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10
Q

Define a nested case control study

A

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

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11
Q

Define a case cohort study

A

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

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12
Q

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

A 
Strength
Consistency
Specificity
Temporality
Biological gradient
Plausibility
Coherence
Experimental evidence
Analogy
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13
Q

What is a crossover trial?

A

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
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14
Q

Define an N-1 trial

A

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

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15
Q

What is the CONSORT statement?

A

Set of recommendations to improve the quality of RCT reports

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16
Q

What are cross sectional surveys good for?

A

Establishing prevalence and association

- NOT causality

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17
Q

What is a disadvantage of a cross sectional survey?

A

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

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18
Q

Define economic analysis

A

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

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19
Q

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

A 
Random sampling
Systematic sampling
Stratified sampling
Cluster sampling
Convenience sampling (prone to bias!)
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20
Q

Define systematic sampling

A

Every nth member of the target population is selected

- Quasi random sampling

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21
Q

Define stratified sampling

A

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

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22
Q

What are the 5 categories of bias

A 
Reporting
Selection
Performance
Observation
Attrition
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23
Q

What are the examples of reporting bias?

A

Literature search bias

Foreign language exclusion

24
Q

What are the examples of selection bias?

A 
Sampling bias (researcher) - e.g Berkson bias
Response bias (subjects)
25
Q

What are the examples of performance bias?

A

Instrument bias

Questionnaire bias

26
Q

What are the examples of observation bias?

A

Interviewer bias
Recall bias
Response bias
Hawthorne effect

27
Q

Define a positive confounder

A

Results in an association between two variables that are not associated

28
Q

Define a negative confounder

A

Masks an association that is present

29
Q

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

A

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

30
Q

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

A

Stratification
Standardisation
Statistical adjustment using multivariate techniques

31
Q

Which statistical technique can achieve stratification during analysis?

A

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

32
Q

When would you use multiple linear regression?

A

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

33
Q

When would you use logistic regression?

A

To minimise the effect of cofounders when variables are binary

34
Q

What are the two types of randomisation methods?

A

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)

35
Q

What are the types of fixed randomisation?

A

Simple
Block
Stratified

36
Q

What is a type of adaptive randomisation?

A

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

37
Q

What are the three main endpoints used in studies?

A

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)

38
Q

Define validity

A

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

39
Q

Define reliability

A

How consistent a test is on repeated measurements

40
Q

What are the types of validity?

A 
Face
Content
Criterion (concurrent & predictive)
Construct (convergent & divergent)
Incremental
41
Q

Define face validity

A

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

42
Q

Define content validity

A

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

43
Q

Define concurrent validity

A

Subtype of criterion validity

The extent to which the test correlates with a measure that has been previously validated

44
Q

Define predictive validity

A

Subtype of criterion validity

The extent to which the test is able to predict something that it should theoretically be able to predict

45
Q

Define convergent validity

A

Subtype of construct validity

Extent to which the test is similar to other tests measuring the same construct

46
Q

Define divergent validity

A

Subtype of construct validity

Extent to which the test is not similar to other tests that are measuring different constructs

47
Q

Define incremental validity

A

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

48
Q

Define intrarater reliability

A

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

49
Q

Define inter-rater reliability

A

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

50
Q

Define test-retest reliability

A

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

51
Q

What test can be used to assess internal consistency?

A

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

52
Q

What is continuous data?

A

Can take any value e.g height

53
Q

What is Cohen’s Kappa

A

Assesses the level of agreement for data that falls into categories

54
Q

What is the Kappa statistic?

A

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

55
Q

What does a Kappa statistic of 0 mean?

A

Agreement between raters is chance only

56
Q

What does a Kappa statistic of 1 mean?

A

Agreement between raters is perfect beyond chance

Statistics! (4 decks)

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