× Expand AP Photo/Seth Wenig

In a major victory for civil rights and civil liberties, a United States District Court Judge has held that the New York City Police Department's (NYPD) stop-and-frisk policies are unconstitutional. Judge Shira Scheindlin's opinion justifying the ruling is a tour de force. Carefully assessing both systematic evidence and the cases of individual litigants, Judge Scheindlin leaves no serious doubt that the NYPD's policies are inconsistent with the fundamental rights guaranteed by the Constitution.

Under current Fourth Amendment law, not all warrantless searches of people in public violate the Constitution. In the landmark 1968 case Terry v. Ohio, Chief Justice Earl Warren affirmed that "stop-and-frisk" searches are indeed "searches" covered by the Fourth Amendment. As he noted in one passage in his ruling-part of which was used as an epigram by Judge Scheindlin-"it is simply fantastic to urge that such a procedure performed in public by a policeman while the citizen stands helpless, perhaps facing a wall with his hands raised, is a 'petty indignity.' It is a serious intrusion upon the sanctity of the person, which may inflict great indignity and arouse strong resentment, and it is not to be undertaken lightly." Nonetheless, Warren's majority opinion held that the "probable cause" required to obtain a legal search warrant is not necessary for a stop-and-frisk search to be considered constitutional. Rather, police officers needed to have a reasonable suspicion ("whether a reasonably prudent man, in the circumstances, would be warranted in the belief that his safety or that of others was in danger") that a suspect poses a dangerous threat.

In theory, this seems like a reasonable compromise. But applying the standard in practice is fraught with potential dangers. Chief Justice Warren warned that "in determining whether the officer acted reasonably in such circumstances, due weight must be given not to his inchoate and unparticularized suspicion or 'hunch.'" But it's hard to avoid the conclusion that vague hunches are in fact responsible for many stop-and-frisk searches. As Justice William O. Douglas warned in his dissent, without ongoing vigilance, it's easy for the stop-and-frisk regime to devolve into a norm where "the police can pick [someone] up whenever they do not like the cut of his jib."

Which brings us to the NYPD's stop-and-frisk program. At the core of the constitutional challenge to the department's practices is a comprehensive study by Professor Jeffrey Fagan at Columbia University. Fagan's study provided overwhelming evidence that New York's aggressive stop-and-frisk policy was arbitrary and discriminatory. The sheer numbers are staggering-more than 5 million searches have been conducted under the current policy. Nearly 90 percent of the searches did not turn up anything that could justify any kind of arrest or summons. Blacks and Latinos comprised 87 percent of those searches.

More in-depth analysis confirms what the general numbers suggest. Fagan's study found that a minimum of 6 percent of searches were "apparently unjustified." As Scheindlin observes, the 6 percent of unjustified stops is a floor rather than a ceiling. Scheindlin made extremely charitable assumptions-including taking the unchallenged reports of officers at face value. The percentage also doesn't consider the occasions in which a stop-and-frisk goes unreported.

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Even if we were to assume that "only" 6 percent of searches were completely unjustifiable, this still represents 200,000 people whose rights were violated. The number of people subject to unjustifiable searches is certainly far higher. For example, Fagan did not classify searches justified by the officer solely based on allegedly "furtive movements" by the suspect, although it is clear that this is reasoning that cannot meet the "reasonable suspicion" standard. Virtually anybody can be accused of "furtive movement," and the standard is so useless that Fagan's study showed that people who displayed "furtive movements" were actually less likely to be arrested than those that did not.

What's even worse is that the arbitrary searches are not distributed randomly. Racial minorities are searched far out of proportion to their percentage of the populations. New York City has defended this by arguing that racial minorities are also disproportionately represented among those arrested for violent crimes. Scheindlin disposes of this defense by noting that since nine out of ten people stopped are innocent, this defense is irrelevant. Moreover, "[t]he NYPD carries out more stops where there are more black and Hispanic residents, even when other relevant variables are held constant." The singling out of racial minorities cannot be justified.

Given the data, Scheindlin had little choice but to find that the stop-and-frisk policy violated the Fourth Amendment as well as the equal protection clause of the 14th Amendment. A large number of searches have been conducted without reasonable suspicion, and these suspicionless searches have disproportionately targeted racial minorities. Of 19 individual stops, the court found that 9 of the stop-and-frisks were unconstitutional, 5 of the frisks after stops were unconstitutional, and 5 were constitutionally permissible.

As MSNBC's Adam Serwer notes, particularly telling is that most defenses of the NYPD's program all but conceded its unconstitutionality. Rather than trying to deny that the program was discriminatory, defenders instead tried to change the subject to the question of whether it was effective. This response is defective for two reasons. First of all, effectiveness is not in itself an adequate defense of an unconstitutional policy. Scheindlin makes this clear: "Many police practices may be useful for fighting crime-preventive detention or coerced confessions, for example-but because they are unconstitutional they cannot be used, no matter how effective."

Even if one were to argue the effectiveness of the policy should cause us to overlook those pesky Fourth and 14th Amendments, the evidence for the NYPD program's effectiveness is very weak. The argument rests on a post hoc ergo propter hoc fallacy-violent crimes rates have dropped in New York, New York has a discriminatory stop-and-frisk program, so the declining crime rates must have been produced by the discriminatory stop-and-frisk program.

There's no reason to make this causal inference. The drop in violent crime rates in New York began well before the current stop-and-frisk program. Violent crime is declining nationally, not just in New York. Violent crime continued to drop in New York in 2012 even as the number of stop-and-frisk searches declined.

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The court was right to intervene. Judge Scheindlin ordered a lawyer to enforce compliance with the Constitution. Unfortunately, Mayor Michael Bloomberg reacted with anger and defiance, vowing to appeal and making baseless claims about the public-safety effects of the ruling. It's not clear if anything will change immediately.

Bloomberg, however, is nearing the end of his term, so there is hope that this important and powerfully argued opinion means that stop-and-frisk will start getting more attention in coverage of the New York City mayoral race than Anthony Weiner's genitals. It is crucial that the next mayor begin to respect the fundamental rights of the city's residents even if the current regime refuses to.