In a study published in Preventive Medicine (1991), researchers Stampfer and Colditz observed that women who underwent hormone replacement therapy (HRT) showed a lower risk of coronary heart disease (CHD).
a. Identify the explanatory and response variables.
b. Identify a confounding variable that provides an alternative explanation for the reduction in CHD risk among women who underwent HRT, compared to those who didn’t undergo HRT. Also, include a diagram showing how this explanation works.