Chief Justice Roberts use of statistics are either phony – or ignorant. You choose!

In oral arguments before the Supreme Court last week, Chief Justice John G. Roberts Jr. introduced a statistical claim that he took to imply that an important provision of the Voting Rights Act has become outmoded.

Section 5 of the Voting Rights Act, which is being challenged by Shelby County, Ala., in the case before the court, requires that certain states, counties and townships with a history of racial discrimination get approval (or “pre-clearance”) from the Department of Justice before making changes to their voting laws. But Chief Justice Roberts said that Mississippi, which is covered by Section 5, has the best ratio of African-American to white turnout, while Massachusetts, which is not covered, has the worst, he said…

As much as it pleases me to see statistical data introduced in the Supreme Court, the act of citing statistical factoids is not the same thing as drawing sound inferences from them…

Like other polls, the Current Population Survey is subject to sampling error, a result of collecting data among a random subsample of the population rather than everyone in the state. In states like Massachusetts that have low African-American populations, the margin of error can be especially high: it was plus-or-minus 9.6 percentage points in estimating the black turnout rate in 2004, according to the Census Bureau. Even in Mississippi, which has a larger black population, the margin of error was 5.2 percentage points…

The debate might be more constructive if we return to the substantive questions that I posed earlier. First, are the voting rates in Massachusetts and Mississippi representative of a broader trend? If so, it seems wrong to suggest that Chief Justice Roberts misconstrued the data merely because he failed to mention the margin of error. But if Massachusetts and Mississippi are outliers, then the chief justice may be guilty…Cherry-picking the evidence…is the greater statistical sin, in my view, since it involves making misleading rather than merely imprecise claims.

The bigger potential flaw with Chief Justice Roberts’s argument is not with the statistics he cites but with the conclusion he draws from them…

…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?…

Statistical analysis can inform the answers if applied thoughtfully. But statistics can obscure the truth when they become divorced from the historical, legal and logical context of a case.

Roberts proved to the world that opportunism holds a higher priority in his pantheon of justice – in his testimony before Congress when he was being confirmed for office. Almost every decision since has reflected that opportunism, lack of forthcoming honesty. A few recent cases may illustrate qualms on his part – I hope.

Regardless, Nate Silver stands as the voice of expert testimony about statistics which the Republican Party learned to their recent dismay.

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