What design feature is used in the arthritis medication experiment to account for age differences among subjects?

Blocking by age is a crucial design feature in the arthritis medication experiment because it helps to control for the confounding variable of age. In this context, age can influence how subjects respond to the medication, potentially leading to variability in the results. By dividing subjects into age groups (blocks), researchers ensure that comparisons are made within groups that are more homogeneous regarding age, thus isolating the treatment effect of the medication more effectively.

This approach allows for a clearer understanding of the medication’s efficacy, as variations due to age differences are minimized. It increases the precision of the experiment and helps to ensure that if any differences in outcomes occur, they can be more confidently attributed to the medication rather than age-related factors. Overall, blocking by age is an effective way to enhance the experiment's validity and reliability.