Interpreting epidemiological findings

Question 1

What are the Bradford hill cirtiera?

Answer 1

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 of errors or fallacies that might befall between studies

Question 4

What does specificity mean?

Answer 4

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

Question 5

What is temporality?

Answer 5

Measuring over time

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

eg 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

Question 14

What is external validity?

Answer 14

Generalisiability

Question 15

What can selection bias also be called?

Answer 15

Berkson’s bias (in hospitals)

Healthy worker effect (occupational studies)

Question 16

How can you avoid selection bias?

Answer 16

Controls representative of target population
Minimise non-response
Compare respondents with non respondents

Question 17

What is information bias?

Answer 17

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

Question 18

What is interviewer bias?

Answer 18

Interviewers ask about exposure status

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 19

What is recall bias?

Answer 19

When people become ill they are more likely to think hard about how past experiences have affected them

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

Question 20

What is non-differential misclassification?

Answer 20

When exposure status is misclassified but equally among controls and cases

Errors in determining outcome in controls and cases

Question 21

What does non-differential misclassification result in?

Answer 21

Bias always towards the null

Question 22

What is confounding?

Answer 22

The effect of an extraneous variable that wholly or partial accounts for the apparent effects of the study exposure, or that masks an underlying true association

Question 23

What can confounding lead to?

Answer 23

Biased estimates

Question 24

How can you identify confounding?

Answer 24

Knowledge of the subject matter

Three conditions for confounding

Stratfication

Question 25

What are the three conditions for confounding?

Answer 25

Associated with the exposure in the source population

Associated with the outcome in the absence of the exposure

Not a consequence of the exposure

Compare crude and adjusted estimates

Only one of the above is necessary

Question 26

How do you conduct stratification?

Answer 26

Compare stratum specific estimates with the estimate you get when you analyse the date from the study

Question 27

What after conducting stratification might indicate confounding:?

Answer 27

Pooled estimate is considerably different from what you expect from stratum specific estimates

Question 28

What is effect modification?

Answer 28

where the magnitude of the effect of an exposure variable on an outcome variable differs depending on a third variable

Question 29

How can you test for effect modification?

Answer 29

Breslow-Day test
Q test
Interaction terms in regression models

Question 30

What is synergism?

Answer 30

The effect modifier potentiates the affect of the exposure

Question 31

What is antagonism?

Answer 31

The effect modifier demeans the effect of the exposure

Question 32

What are adjusted models used for?

Answer 32

Identification of potential confounding

And used to account for it

Question 33

What is a crude model?

Answer 33

univariate analysis of exposure vs outcome

Question 34

What does the crude model do?

Answer 34

simply looks at the impact of the exposure on the outcome – with no consideration of anything else

Question 35

What is an adjusted model?

Answer 35

multivariate analysis of a range of exposures vs. outcome

Question 36

What is multivariate analysis?

Answer 36

multiple potential exposures have been included. The inference is that the outputs of these analyses mean that holding all other adjusted variables equal, X is the association between exposure and outcome

Question 37

What are other ways of naming crude vs adjusted models?

Answer 37

Hazard ratio (HR) vs Adjusted Hazard Ratio (Adj. HR) 
Odds ratio (OR) vs Adjusted odds ratio (AOR) 
Univariate model vs multivariate model