Harry A. Blackmun

Summary: Harry A. Blackmun was a U.S. Supreme Court justice who applied mathematical logic in his judicial career.

Harry A. Blackmun (1908–1999) is best known as the author of the majority opinion in Roe v. Wade, the U.S. Supreme Court case that recognized a constitutional right to abortion. Blackmun, however, was perhaps the only Supreme Court justice to hold a degree in mathematics (A.B., Harvard, 1929), and one of the very few who has carefully applied mathematical concepts in judicial opinions.

Blackmun graduated from Harvard Law School in 1932 and served as law clerk to Judge John B. Sanborn of the U.S. Court of Appeals for the Eighth Circuit. His law practice, with a prominent Minneapolis law firm and the Mayo Clinic, focused primarily on tax law and estate planning. He succeeded Judge Sanborn on the Eighth Circuit in 1959 and was appointed to the U.S. Supreme Court by President Richard M. Nixon in 1970 following the Senate’s rejection of two previous nominees. Both of Blackmun’s judicial appointments were promoted by his childhood friend, Chief Justice Warren E. Burger. So close was this connection that for their first decade on the Supreme Court, the two men were referred to as the “Minnesota Twins,” but thereafter they went separate jurisprudential ways.

Blackmun and Mathematical Reasoning

A particularly striking example of Blackmun’s use of mathematical reasoning involves his application of the binomial distributionas a method for assessing discrimination claims. In Castaneda v. Partida (1977), a Texas county was accused of systematically discriminating against Mexican Americans in the selection of grand jurors. Mexican Americans constituted nearly 80% of the population but only 39% of the grand jurors during the 11-year period at issue. Blackmun’s opinion for the Court noted the substantial absolute disparity but used the binomial distribution to explain the unlikelihood that such a disparity would have arisen by chance. Eschewing mathematical symbols, he verbally explained the calculations involved and the formula for making them. The difference between the observed and the expected number of Mexican-American grand jurors during this period was approximately 29 standard deviations, a result that would occur by chance less than once in 10149 times. The use of statistical evidence has since become standard practice in discrimination cases.

Justice Blackmun also relied heavily on empirical evidence in Ballew v. Georgia (1978), a case that established the minimum constitutionally acceptable size for juries. American juries traditionally had 12 members, but—in a case considered shortly before Blackmun took his seat—the Supreme Court held that six-member juries were permissible. Ballew held that a five-person jury was too small to satisfy the requirements of due process. Blackmun’s opinion on this issue spoke for all of his colleagues, some of whom wrote separately on other issues. Engaging with a substantial body of statistical and experimental research, he observed that smaller juries are less likely to engage in effective deliberations, take diverse viewpoints seriously, and reflect a fair cross-section of the community than 12-person juries and that smaller juries are more likely to reach inaccurate judgments. Blackmun conceded that the differences between five- and six-person juries might be difficult to discern empirically, but he concluded that a line had to be drawn somewhere to avoid further reductions in jury size. The data actually raised troubling questions about the earlier decision upholding six-person juries, but the Court was unwilling to overrule that precedent.

Finally, Blackmun addressed statistical issues relating to the imposition of the death penalty, both on the Supreme Court and on the court of appeals. On the Eighth Circuit, in Maxwell v. Bishop (1968), Blackmun rejected a statistical study purporting to show that African Americans were much more likely than whites to get the death penalty in rape cases. The study was limited in scope, did not relate to the county where the case arose, failed to account for relevant variables, and did not show that racism affected the verdict or sentence in that case. The Supreme Court set aside this decision because of an intervening ruling on a different issue.

Two decades later, in McCleskey v. Kemp (1987), Blackmun dissented from a decision that rejected a claim of racial discrimination in a Georgia death penalty case. Blackmun explained that this claim was supported by a multiple regression analysis of every homicide case in that state during the relevant time period. The study, which included 230 variables, found that persons accused of killing whites were 4.3 times as likely to receive a death sentence as persons accused of killing African Americans and that African-American defendants were significantly more likely to be sentenced to death than white defendants. Blackmun emphasized the “sophistication and detail” of this study and concluded that it showed an unacceptable risk that racism had affected the decision to impose the death sentence.

Bibliography

Greenhouse, Linda. Becoming Justice Blackmun: Harry Blackmun’s Supreme Court Journey. New York: Times Books, 2005.

Yarbrough, Tinsley E. Harry A. Blackmun: The Outsider Justice. New York: Oxford University Press, 2008.