Suggested answer to exercise: House dust mite and wheeze in Ethiopia, 2

Question 2: What is an interaction? How would they test for an interaction between urban-rural living and house dust mite skin sensitisation?

Suggested answer

An interaction means that the effect of a predictor variable depends on the value of another, here that house dust mite sensitisation is a much better predictor of wheeze in urban areas than rural areas. They would test for it by including an extra variable in a logistic regression, equal to one for house dust mite sensitive people in urban areas, zero otherwise. Alternatively, if urban is coded one, rural zero, and house dust mite sensitivity is one for sensitive and zero for not sensitive, the interaction variable is found by multiplying these two variables together.

Back to Exercise: House dust mite and wheeze in Ethiopia.

To Clinical Biostatistics index.

To Martin Bland's M.Sc. index.

To Martin Bland's home page.

This page maintained by Martin Bland.
Last updated: 31 July, 2006.

Back to top.