"Quickie Correlations on Crime and Punishment Stats"

Kent Scheidegger has this post at Crime & Consequences. In part:

My quickie spreadsheet calculation shows a coefficient of correlation between violent crime rate and prisoner change of -0.27.  For property crime it is -0.31.  If we use numbers of crimes instead of rates, the correlations are a tad stronger.

A negative correlation means that the two variables tend to move in opposite directions.  As number of prisoners goes down, crimes tend to go up.  That is just what persons of sense would expect.