The Beauty of Tautological Cycles

Missing on a random is the example that I gave you when I don't give you my weight. You can't tell specifically if people of a certain weight are less likely to provide information about their weight or not because you don't have those particular data. When your data are missing not at random, then potentially you're in a bad, bad place. If you want to know anything about missing data, just go get Craig Ender's book gets everything that you you need to know about missing data.