In Example 13.11 (page 410) on quality of life with treatments for alcohol dependence, suppose that subjects who drop out of the study become, over time, less financially satisfied.

(a) Explain why the missing at random assumption would be violated.

(b) Explain why the time effect may be overestimated using only the data observed.

(c) Describe a dropout pattern such that estimates of the treatment effect would be biased.