Mandatory sentencing

In the 80's mandatory sentencing laws came on the books but to find any correlation between those laws and the decrease in crime is difficult at best. There are countless articles on the subject but none specifically state that tougher sentences results in lower crime. This is somewhat of a mystery because of two facts that are readily available on line. The U.S. federal prison population has increased almost 790 percent since 1980 from about 25,000 inmates to 219,000 in 2012, according to a new Congressional Research Service report. Violent crime was 600 per 100,000 people in 1980 and 365 per 100,000 in 2012. One would think that just by looking at those two statistics a good correlation could be drawn demonstrating that tougher laws means lower crime but it is not there. Some would say it doesn't fit the narrative of those who oppose tougher crime laws.