KLMED8008 Repeated measurements

The exercises are voluntary and do not need to be handed in. However, they are revelant for the final one-week take-home exam. Lecturer are present to provide assistance and guidance.

Exercise 1

1. Textbook, Exercise 1.2 (anorexia.dta, p 41 in 2nd ed., p 61 in 3rd ed., p 64 in 4th ed.)

2. To estimate sample sizes in an experiment in which two groups are compared and the outcome is adjusted for baseline, run the following Stata commands:

sampsi 55 60, sd(15) pre(1) r01(0.55)
sampsi 55 60, sd(15) pre(1) r01(0.35)

The only difference is that the correlation between baseline and outcome variables differs (0.55 vs. 0.35). You may wish to try other values as well.
Verify by inspection that the best (more effective) analysis strategy in each case is "ANCOVA".
Try to explain why the "change" strategy (i.e. paired t-test) is ineffective - and in fact worse than the "post" strategy - when correlation is low.

3. Textbook, Exercise 2.7 (birthwt.dta, p 89-90 in 2nd ed., p 119-120 in 3rd ed., p 130 in 4th ed)