# Effect modification. Flashcards

When does Effect Modification occur?

When the strength of association varies over different categories of a third variable in an association study.

Name four examples of effect modifiers?

- Sex.
- Age.
- Environmental exposure.
- Genetic effect.

Do you modify for effect modification?

No. It is not an error.

What OR’s do you look at when looking at effect modification?

Stratum specific OR’s.

How do you evaluate stratum specific OR’s?

- Calculate P values on homogeneity tests.

2. Evaluate overlap of CI’s on stratum specific OR’s.

What homogeneity test do you use to calculate the p values for effect modification?

Breslow-day test.

What is the conceptual definition of an effect modifier?

The effect of the exposure and potential modifier differ from the expected joint effect.

What is synergism?

Effect modifier extenuates the effect of an exposure.

Antagonism?

Effect modifier diminishes/eliminates the effect of the exposure.

For something to be an effect modifier what must the OR be after stratifying?

Statistically different.

When will an effect modifier be described as being in the ‘grey zone’ what is overlapping?

The confidence intervals.

Apart from using the Mantel-Haenzsel OR what other way can you adjust for confounding?

Report confounders separately.

What is the equation for the null hypothesis for the Mantel-Haenzsel test?

H0= OR1=OR2

What is the alternative hypothesis for the Mantel-Haenzsel test?

H1= OR1 is not equal to OR2.

What distribution is used in the Mantel-Haenzsel test?

Chi squared to 1 dof.

In words what is the null hypothesis for the Mantel-Haenzsel test?

Stratum specific OR’s are homogenous.

What is not considered in the Breslow-Day test?

Ordering in the strata.

Why is it difficult to stratify by multiple variables in the Breslow-Day test?

Data becomes sparse.

Can you control for additional covariates in the Breslow-day test?

No.