Causality and the Voting Rights Act

The Supreme Court is currently hearing a case that challenges Section 5 of the Voting Rights Act of 1965. Section 5 requires states, counties and townships with a history of racial discrimination to get pre-approval from the US Justice Department before making changes to their existing voting laws. NY Times columnist and statistician Nate Silver recently wrote a post (here) on the statistical fallacies being offered in court to demonstrate that the Voting Rights Act is no longer needed.

In oral arguments before the court (here), Justice Roberts made some questionable comparisons between percentage of Black voters in Mississippi and Massachusetts to argue that the Voting Rights Act is no longer needed (Black voting percentages are currently higher in Mississippi). Nate Silver points out that selecting two (possibly outlier) States for comparison is basically cherry picking. Silver goes on to conclude:

... the fact that black turnout rates are now roughly as high in states covered by Section 5 might be taken as evidence that the Voting Rights Act has been effective. There were huge regional differences in black turnout rates in the early 1960s, before the Voting Rights Act was passed. (In the 1964 election, for example, nonwhite turnout was about 45 percent in the South, but close to 70 percent elsewhere in the country.) These differences have largely evaporated now.

How much of this is because of the Voting Rights Act, as opposed to other voter protections that have been adopted since that time, or other societal changes? And even if the Voting Rights Act has been important in facilitating the changes, how many of the gains might be lost if the Section 5 requirements were dropped now?

These are difficult questions that the Supreme Court faces. They are questions of causality – and as any good lawyer knows, establishing a chain of causality is often the most difficult chore in a case.

I would like to pick up on the point about causality.  From the directed graph above and using Judea Pearl's notation, the Voting Rights Act was an experimental manipulation (Pearl's "do" notation) of voting laws in States with a history of racial discrimination and voter suppression. From the standpoint of causality, the issue does not involve increases in Black Turnout. The important question is whether Right Wing Voter Suppression and racial discrimination has ended. If the forces that have reduced Black Turnout have not changed then removing the Voting Rights Act will suppress Black Turnout again.

What evidence do we have about Right Wing Voter Suppression? We have the last presidential election when the Republican party actively attempted to suppress minority voting in an attempt to win the election for Mitt Romney. Does anyone think this will be obvious to the Right Wing Justices on the Supreme Court?