Question

Does living in the South cause high blood pressure? Data from a group of 6278 whites and blacks questioned in the Third National Health and Nutritional Examination Survey between 1988 and 1994 (see CNN.com web site article of January 6,2000 , titled "High Blood Pressure Greater Risk in U.S. South, Study Says") indicates that a greater percentage of Southerners have high blood pressure than do people in any other region of the United States. This difference in rate of high blood pressure was found in every ethnic group, gender, and age category studied. List at least two possible reasons we cannot conclude that living in the South causes high blood pressure.

Short answer

We cannot conclude that living in the South causes high blood pressure, due to the possibility of confounding variables which might not be accounted for. Furthermore, the correlation might merely be a result of Reverse Causation.

Step-by-step solution

Understand the Correlation-Causation Fallacy

Just because two phenomena are correlated does not mean that one causes the other. The relationship between location and high blood pressure in this case could be an example of correlation, but not necessarily causation. It is necessary first to critically consider other variables that could be influencing the data.

Identify the Confounding Variables

There might be some confounding variables not accounted for in this study. For instance, climate differences, dietary habits, level of physical activity, stress level, healthcare access, etc., all contribute to blood pressure level. These variables cluster differently in different locations. In the South, if the locals, irrespective of their ethnic group, gender and age, share certain lifestyle habits that predispose to high blood pressure, it would give the appearance of geographical location (the South) causing high blood pressure.

Address the issue of Reverse Causation

The idea of Reverse Causation is also crucial in this form of analysis, where the supposed 'effect' might actually be the 'cause'. In illustration, those with high blood pressure might move to the South due to factors like climate, which they perceive as being beneficial to their health. This would inflate the numbers of hypertensive individuals living in the South, making it appear as though living in the South causes high blood pressure.