Interpreting Epidemiological Findings (1)

Question 1

What are the terminology of Bradford hill criteria?

Answer 1

association vs causation

• criteria used to enable us to infer causation from observational and interventional methods

Strength
Consistency
Specificity
Temporality
Biological Gradient
Plausibility
Coherence
Experiment
Analogy

Question 2

What does strength mean?

Answer 2

A stronger association increases the confidence that an exposure causes an outcome

Question 3

What does consistency mean?

Answer 3

Consistent findings across settings tends to rule out errors or fallacies that might befall between studies

Question 4

What does specificity mean?

Answer 4

describes an association between specific causes and specific events
If not specific – doesn’t mean invalidity! (esp. with multifactorial issues)

Specificity can be informative when present but its absence convey very little

Question 5

What is temporality?

Answer 5

Measuring over time

the exposure should commonly precede the outcome
Hard to assess with cross sectional studies

Question 6

What is biological gradient?

Answer 6

A dose-response effect is a compelling argument for causality

e.g. consuming more cigarettes increases likelihood of disease

Question 7

What is plausibility?

Answer 7

Relationship should be biologically plausible where the science is understood

Question 8

What is coherence?

Answer 8

The association ought to be consistent with the existing theory and knowledge

Question 9

What is experiment?

Answer 9

Evidence from experimentation should be supportive of the proposed link

Question 10

What is analogy?

Answer 10

Drawing upon analogous findings, we many make inference on the relationship

e.g. rubella causes deafness so you could consider that other viruses can cause similar issues

Question 11

What is bias?

Answer 11

Any trends in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systematically different from the truth

Question 12

What are the three types of bias?

Answer 12

Selection
Information
Compounding

Question 13

What is internal validity?

Answer 13

The extent to which findings accurately describe the relationship between exposure and outcome in the context of the study

-when association truly exists within study participants

Question 14

What is external validity?

Answer 14

Generalisability

-when association observed within a study can be extended to the wider population

Question 15

What can selection bias also be called?

What is selection bias?

How can you avoid selection bias?

Answer 15

Berkson’s bias – hospital based - case control study w/controls selected among the hospital’s patients

Healthy worker effect – active workers are more likely to be healthy than those who have stopped working (occupational studies)

Occurs when individuals or groups in a study differ systematically from target population leading to a systematic error in an association or outcome - When participation in a study is associated with the exposure and the outcome

to miminimse:

• Controls representative of target population
• Minimise non-response (i.e declining to participate)
• Compare respondents with non respondents

Question 16

What is information bias?

Answer 16

Due to a number reasons we have misclassification of the exposure or disease status (or both)

Can include: interviewer, recall, response, and diagnostic bias

Due to ill-defined variables/flaws in data collection

Flaws in data collection

• Interviewer bias
• Recall bias

Question 17

What is interviewer bias?

Answer 17

Interviewers ask about exposure status -

= Prevented by interviewer being blind/strict protocol when collecting data

Might be more thorough in interviewing on a related topic if disease status is known

e.g. smoking history in those with lung cancer

Question 18

What is recall bias?

Answer 18

When people become ill they are more likely to think hard about how past experiences have affected them - – bias when participants self report exposures between cases and controls
= Prevent with objective ways to assess exposure

e.g. more likely to remember a brief period of smoking many years ago if you have been diagnosed with lung cancer

Question 19

What is non-differential misclassification?

Answer 19

When exposure status is misclassified but equally among controls and cases

Errors in determining outcome in controls and cases

Bias always towards the null

Question 20

What is differential misclassification?

Answer 20

Misclassification of exposure is not equal between cases and controls (disproportionate)

-Bias towards or away from the null

Question 21

2 types of misclassification

Answer 21

non differential and differential

Question 22

Key points

Answer 22

a. An epidemiologically sceptical approach requires us to rule out chance, bias (including
confounding) before we infer a real relationship – whether causal or not.
b. When assessing the validity of a study, we examine both its internal validity and its
generalisability (external validity) when interpreting findings.
c. There are nine Bradford Hill criteria that can be used to infer causality or absence
thereof. Their application is not a precise science but requires judgment and critical
thinking.
d. In addition to confounding, there are two major groups of bias: selection bias and
information bias.
e. Association does not equal causation.

Question 23

which type of bias is described as Misclassification of the exposure, outcome or both.

Answer 23

information bias

Question 24

the following are all types of which bias?
Recall bias 
Response bias 
Interviewer bias 
Diagnostic bias

Answer 24

information bias

Question 25

Healthy worker effect is a type of which bias

Answer 25

Selection bias

Question 26

Where cases and controls equally mis-report their exposures, this would likely be described as:

Answer 26

Non differential misclassification

Question 27

if cases or controls were likely to report exposures differentially then it would:

Answer 27

differential misclassification.

Question 28

Non differential misclassification always leads to an association that is biased:

Answer 28

towards the null

Question 29

Where cases and controls unequally mis-report their exposures AND in such a way that the overall consequence is an association that tends away from the null, this is best described as:

Answer 29

information bias

Question 30

term to describe:
The extent to which findings accurately describe the relationship between exposure and outcome in the context of the study

Answer 30

Internal validity

Question 31

External validity is synonymous with:

Answer 31

Genralisability

Question 32

A study, which is designed very well, and implemented equally well - but which is carried out a single teaching hospital in London can be said to have high:

Answer 32

internal validity

Question 33

The findings of a study which is designed well but which loses more participants than expected are submitted for peer review. Which of the following might be called into question by the peer reviewers?

Answer 33

internal validity lacking

Question 34

The findings of a study which is designed poorly but implemented exceptionally well, is submitted for peer review. Which of the following might be called into question by the peer reviewers?

internal validity
external validity

Answer 34

internal validity - due to poor design

Question 35

An international multicentre randomised controlled trial with triple blinding is reported in the literature. On the basis of this sentence alone, which of the following is more likely?

Good internal validity
Good external validity

Answer 35

good external validity

Question 36

which type of bias are the following types of:

Healthy worker effect
Non-response bias

Answer 36

Selection bias

Question 37

What is the Healthy Worker Effect

Answer 37

how employed persons are generally more healthy than those who are unemployed.

Question 38

What is response bias

Answer 38

the tendency of participants to respond to questions in a way that is more socially acceptable.

Question 39

What is non-response bias

Answer 39

the process through which people who do not respond are systematically different to the people who do respond. This is a type of selection bias.

Question 40

describe the lake woebegone effect

Answer 40

• referred to as illusory superiority.
  eg. If you ask a class of students how good their driving is, most of them will believe themselves to be better than average.

Question 41

describe the hawthorne effects

Answer 41

The precise definition is controversial
- usually described as the consequence of participants realising they are being observed and therefore acting differently. For example, if you knew you were being studied, you might behave in a slightly different way to normal!