Interpreting Epidemiological Findings (2)

Question 1

What is confounding?

Answer 1

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

Question 2

What can confounding lead to?

Answer 2

Biased estimates

Question 3

How can you identify confounding?

Answer 3

Knowledge of the subject matter: you could undertake an evidence review and see what other people have proposed or found

Test by the three criteria: associated with exposure in the source population; associated with the outcome in the absence of the exposure; not a consequence of the exposure

Stratification: we can look at the difference of apparent effect within different population strata

Compare the crude and adjust statistical estimate

Question 4

What are the three conditions for confounding?

Answer 4

Associated with the exposure in the source population

Associated with the outcome in the absence of the exposure

Not a consequence of the exposure

Question 5

How do you conduct stratification?

Answer 5

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

Question 6

What after conducting stratification might indicate confounding?

Answer 6

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

Question 7

What is effect modification?

Answer 7

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

Question 8

How can you test for effect modification?

Answer 8

Breslow-Day test
Q test
Interaction terms in regression models

Question 9

What is synergism?

Answer 9

The effect modifier potentiates the affect of the exposure

Question 10

What is antagonism?

Answer 10

The effect modifier demeans the effect of the exposure

Question 11

What are adjusted models used for?

Answer 11

Identification of potential confounding

And used to account for it

Question 12

What is a crude model?

Answer 12

Univariate analysis of exposure vs outcome

Question 13

What does the crude model do?

Answer 13

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

Question 14

What is an adjusted model?

Answer 14

Multivariate analysis of a range of exposures vs. outcome

Question 15

What is multivariate analysis?

Answer 15

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 16

What are other ways of naming crude vs adjusted models?

Answer 16

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