Simpson's Paradox: An Example From a Longitudinal Study in South Africa

Abstract

Real world examples of the reversal of the direction of an association when an additional explanatory variable is taken into account are unusual and hard to find. This article presents an example of Simpson's paradox from a South African longitudinal study of growth of children. The example demonstrates the importance race plays in every aspect of South African life.

Keywords:

• Categorical data
• Comparing proportions

Acknowledgments

I thank the Birth to Ten Study and the Chronic Diseases of Lifestyle Programme at the Medical Research Council in Cape Town, South Africa, for the use of these data.