I have taught many statistics courses over the years and have long been of the opinion that, if my students don't understand, then I haven't adequately explained the issues. The same applies here. It seems to me that, as citizens in an increasingly data-driven society, how we are to discriminate between the ephemeral and the substantive becomes an increasingly important question.
All decisions based on test scores and interpretations of data analyses are subject to error.
Largely though these analyses and data remain unquestioned and, as a result, largely invisible, something akin to the net's urban legends, stories simply accepted as true. We do so at considerable peril. Just so, it's prudent to establish that a model fits the data before interpreting any results. The Bell Curve analysis. In this section, you'll find the program I ran to read HM's data, compute new variables, and run analyses.