Missing data, part 1. Why missing data are a problem

Missing data, part 2. Missing data mechanisms: Missing completely at random, missing at random, missing not at random, and why they matter

“…n the first article, 1 we demonstrated that any analysis with missing data makes untestable assumptions about the missing values. The use of different statistical methods rests on different missing data assumptions, and it is important to be transparent about which assumption we are making when implementing a given method.…”