# Confounding/ controlling for confounding. Flashcards

At what stage(s) of the study can confounding be corrected for?

The design or analysis stage.

What is a crude association?

An association between an exposure and an outcome before adjusting for any confounders.

Describe what is meant by confounding.

An extraneous variable that is a common cause of an exposure and outcome that fully or partially explains the observed effect.

What three conditions need to be satisfied at the data analysis stage for something to be a confounder?

- Association with the study exposure in the control group.
- Associated with the disease in the unexposed group.
- Not on the causal pathway for exposure-disease.

If you stratify by a potential confounder (in this case smoking) what will the H0 be?

ORnonsmoke = ORsmoke.

What is a Mantel-Haenazel OR and how is it used?

A OR adjusted for a confounding variable. This will take into account the weighted averages of the separate OR’s of the confounding groups. This adjusted OR can then be compared to the crude OR. if there is a roughly 15% different the factor can then be counted as a confounder.

You only need to correct for confounders if the Mantel-Haenazel ratio is 15% different from the crude OR. True or false?

False. You should still correct for a confounding factor as it is still an error, even if it is not technically classes as a confounder.

If the analysis of data suggests that there is no confounding effect you should accept that there is no cofounding effect, even if literature says that something may be a biologically confounding factor. This is because the statistical analysis is more robust. True or false?

False. The causal definition is the most important thing to consider when deciding wether if something is a confounder.

If the analysis of data suggests that there is a confounding effect you should accept that there is a cofounding effect, even if past literature says that something is not a biologically confounding factor. This is because the statistical analysis is more robust. True or false?

False. The causal definition is the most important thing to consider when deciding wether if something is a confounder.

What is the limiting factor when using the causal definition in deciding whether something is a confounding factor?

Current biological knowledge.

It is not ideal to adjust for every single factor that could be confounding. Why? (2 reasons).

- Efficiency is reduced.

2. Confidence intervals become wider.

If you adjust for a non confounder what can it produce?

Additional bias.

What sort of confounding is this?

crude odd > adjusted odd.

Positive confounding.

What sort of confounding is this?

crude odd < adjusted odd.

Negative confounding.

What is qualitative confounding?

When one OR is less than 1 and one is more than 1.