Right To Work and Unemployment

There is a raging debate in Michigan now over "Right To Work" laws, which are being proposed by the Republican controlled state legislature.  RTW would allow workers in a union shop to refuse to pay dues if they don't want to be members.

This chart, which I made, is a histogram of unemployment rates (as of Oct 2012) in Right To Work ("RTW") and Forced Union ("FU") states.

As you can see, RTW states have a lower distribution of unemployment rate, and FU states skew higher.

Now, correlation does not necessarily mean causation... but the trend is clear.  RTW states have lower unemployment rates.