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Two major statistical declines related to homicide have occurred during the past two decades that could prove instructive for those involved in murder prevention, say two MIT researchers.
They cited these patterns based on national murder statistics and homicide data for 100 large American cities in the 20 years from 1973 to 1992:
Murders by and against US black males 25 and older fell sharply from the early 1970s to the early 1990s.
Murder in US cities dropped just as much in the four-year period 1980-84 as it rose in the troubled eight-year span 1984-92.
In a new report titled "Urban Homicide: Opportunity Knocks?" Dr. Arnold Barnett and Jesse Goranson contend that few Americans know that these huge declines took place, let alone understand why they occurred.
Dr. Barnett, professor of operations research/statistics at MIT's Sloan School of Management, is the author of several widely reported studies on such topics as air safety, voting patterns, war casualties and urban homicide risk. Mr. Goranson, who holds bachelor's and master's degrees from MIT, now works at Gemini Consulting.
They argue that Americans "need to know more" about the substantial drop in murder rates during the last two decades, a period that also contained some major and well-known surges in killing.
If it can be determined what forces caused the declines in murder, they suggest, perhaps these forces can be harnessed to reduce homicide rates today.
"Recent US murder trends have been more divergent than unrelievedly bleak, but we find it far easier to identify cities, periods and demographic groups in which homicide rates are rising than in which they are falling. There have been recent declines, however, and they have been massive," the study states.
In the case of murders by blacks, the researchers write "Given the grim news from the inner cities, it might widely be assumed that homicide is growing among blacks. That assumption, however, is apparently incorrect."
Over the past two decades from 1973 to 1992, they note, the increase in murder among black males aged 14-24 has been counteracted by a large decline in killings involving black males 25 and older. In the latter group, the murder arrest rate dropped by half, from approximately 80 arrests per 100,000 citizens per year to 40 arrests per 100,000. Concurrently, the murder victimization rate for black males 25 and older dropped by 35 percent, from roughly 90 per 100,000 citizens per year to 60 per 100,000. And the age range that experienced the decline contained three times as many people in 1990 as the range 14-24 that showed the increase. (In all ethnic groups, killings by males dwarf killings by females.)
While conceding that homicide arrest data are imperfect measures of murder commission patterns, Barnett and Goranson contend that arrest statistics are the best overall barometers we have. "It is hard to imagine that the 50 percent drop in the adult black male arrest rate is not meaningful," they argue, "especially when the national murder arrest rate (arrests per 100,000 residents) did not decline between the early 1970s and the early 1990s."
Cross-city data tell a similar story about race, says the report. The nationally known "homicide epidemic" in Washington, DC is highly atypical of heavily black cities, and Cleveland-with as many blacks as whites-had one of the nation's sharpest declines in murder over 1973-92.
Even among blacks aged 14-24, the authors note, murder was dropping just as fast over 1973-85 as among their elders. Barnett and Goranson state that the more recent rise in killing among young blacks "surely deserves attention," but they declare that it "diverges from the bulk of recent black experience." The authors suggest that greater awareness of that fact "could benefit both policy and race relations."
Barnett and Goranson also call attention to the steep decline in US murder rates in the early 1980s, when murder rates dropped 23 percent between 1980 and 1984. While some people have attributed the drop to the aging of the post-World War II baby boom beyond the main "homicide prone" years, the authors' calculations imply that such an explanation is highly inadequate: adjusting for the demographic change only slightly affects the overall decline.
The 1980-84 decline is especially curious, according to the researchers, because it occurred while "the nation suffered its worst economic downturn since the Great Depression and while a president often viewed as unsympathetic to the cities substantially cut the federal aid that they received." Barnett and Goranson say that Americans may "think (they) know what has gone wrong since the mid-1980s (drugs, gangs, guns)," but the authors ask whether "we have any idea what was going right in the preceding four years?"
The researchers focused in detail on 100 of the 250 largest US cities: the largest 25, every other city from the next 50 largest, every third city from the next 75 and every fourth from the next 100. (That selection rule gives greater weight to large cities without letting them utterly dominate the calculations.)
They found a divergent 20-year pattern of urban homicide in which there was almost no net trend over 1973-92. After adjustments for demographic factors like the age distribution, the 100-city average murder rate rose by about one-third of one percent per year over the 20-year period. Between 1980 and 1992, the rate rose in total by only one percent. (Nationally, the murder rate was totally unchanged over the 20 years; it was 9.3 killings per 100,000 citizens in both 1973 and 1992.)
The authors acknowlege, however, that the overall US murder picture is grim. They report that New York City has far more homicides per year than not just Tokyo but all of Japan, and that, with 20 percent fewer residents than the Republic of Ireland, Chicago has 30 times the number of annual murders. They note that, if recent patterns prevail, homicide will be the cause of death of two percent of all large-city residents, three percent of large-city males, and five percent of large-city black males born this year in the US.
These sobering facts, say the authors, make it all the more urgent to investigate the recent but unheralded declines in US murder.
If it can be determined why-despite the many problems facing the black community-homicide fell sharply among black male adults, "we might be better able to avert future killings," say the researchers. And they warn that "unless we know what conditions discouraged murder in the early 1980s, we can't act to replicate them in the mid-1990s."
An opportunity may be at hand, say Barnett and Goranson, and seizing it is of the greatest importance because "so many lives are at stake."
A version of this article appeared in the August 17, 1994 issue of MIT Tech Talk (Volume 39, Number 2).