Data in justice department filing quoted by Samuel Alito in his opinion relied on unusual methodology, a Guardian analysis has found

The claims Samuel Alito, a supreme court justice, made about voter turnout in Louisiana in a landmark Voting Rights Act case were based on a misleading data analysis, a Guardian review has found.

In his opinion gutting section 2 of the Voting Rights Act last week, Alito said that Black voter turnout had exceeded white voter turnout in two of the five most recent presidential elections, both nationally and in Louisiana. Alito’s claim was copied almost verbatim from a friend-of-the-court brief filed by the justice department. It was a critical data point Alito used to make the argument that the kind of discrimination that once made the Voting Rights Act necessary no longer exists.

But a review of turnout and racial data in Louisiana reveals that assertion relies on an unusual methodology. The justice department brief that Alito cited calculated Black and white voter turnout in Louisiana as a proportion of the total population of each racial group over the age of 18. Such an approach is not preferred by experts in calculating statewide turnout because the general over-18 population may include non-citizens, people with felony convictions and others who cannot legally vote.But it does yield Alito’s conclusion that Black voter turnout exceeded white voter turnout in the 2012 and 2016 presidential elections in Louisiana.