I noted last July, just following Boston’s stunning Independence Day surge in homicide, that certain days during the year tend to produce crime spikes. Violence frequently erupts by virtue of the usual activities (e.g., drinking, carousing, and partying with friends) that are associated with particular legal holidays and other unofficial occasions for diversion.

As shown in the chart below, the aggregate number of serious violent crimes (homicide, forcible rape, robbery and aggravated assault) in Boston for 2006 through 2009 spiked significantly upward on three specific dates--January 1, July 4 and October 31.

The latest report from the Bureau of Labor Statistics appears to have good news with regard to the safety and well-being of American workers. According to preliminary tabulations of occupational fatalities for 2010 (see below), homicides in the workplace declined almost 7% over 2009, continuing a long-term downward trend that began nearly two decades ago. In fact, the 506 workplace homicides for 2010 is the lowest count since these statistics have been collected.

Workplace homicides typically involve robbery -- predominately robberies of convenience stores and taxi drivers for quick cash and quick getaway. These types of episodes have indeed declined substantially in recent years, paralleling the general decline in the overall U.S. homicide rate.

The aggregate figures, although encouraging, obscure a troubling fact: Certain forms of workplace homicide -- fatal assaults by co-workers and especially by customers -- continue to buck the overall downward trend (see below).

From City Hall to Grove Hall have come expressions of outrage over the violent crime spree that spoiled the Fourth of July for residents in Roxbury, Dorchester and Mattapan, especially the families of the four men who died from gunfire.

Although the anger, frustration and shock are absolutely justified and understandable, we should not be overly surprised by the Independence Day bloodshed. Hot weather, a day without the structure of work or school, and, of course, alcohol provide a dangerous mix, resulting in a spike in crime seen time and time again.

According to a recent New York Times headline, ("Steady Decline in Major Crime Baffles Experts," May 26, 2011), we criminologists are clueless when it comes to explaining the drop in serious crime. To the contrary, a range of plausible explanations have been advanced to account for the downturn in lawlessness that this nation has enjoyed since the early 1990s. Over the long-term, the welcomed trend can be linked to several factors:

• the calmer aftermath of the late-1980s crack epidemic that had caused city crime levels to spike until the drug market shifted;

• improved police strategies that rely heavily on innovative technology and sophisticated crime analysis tools;

• expanded use of incarceration along with longer sentences that have kept more criminals off the streets; and

• the graying of America whereby the fastest growing segment of the population are the aging "baby-boomers" who are now over 50 years old and hardly babies anymore.

Reading beyond the headline of the Times story, however, what "baffled" me and other criminologists was the short-term plunge in crime from the first half of 2009 to the first half of 2010, especially the 6.2% drop in violent crime that included a 7.1% dip in murder. There is nothing even close to definitive that can account for such a large reduction over such a limited time period (other than the natural fluctuations inherent of short-term trends).

In the days since the Times article appeared, I have been treated to a large volume of e-mails from folks offering various suggestions concerning the cause—everything from the impact of a meeting some five years ago of a large group of transcendental meditators who used their special skills to bring about peace, to an increased community cohesion as the recession prevented countless Americans from moving residences.

More than a few of the e-mailers, however, were riders on the abortion-crime link bandwagon. A spirited debate among economists was ignited a decade ago when John Donohue of Yale and Steven Levitt of the University of Chicago concluded that legalized abortion had produced a drop in crime. These prominent scholars argued that following the 1973 decision in Roe v. Wade, thousands of unwanted fetuses were aborted instead of being born into less-than-ideal environments, thereby producing two decades later a reduction in the pool of at-risk, violence-prone individuals.

At least based on comments uploaded to my "Why mothers kill" blog post of last week, there appears to be some disagreement about whether mothers or fathers are more apt to commit infanticide. The opposing positions are supported by conflicting research reports that use different data sources and different time frames.

There are logical reasons to back either point of view. One might think that fathers are more inclined to kill their children in light of the very uneven gender split generally among those who commit homicide. Overall, 90% of murderers in this country are male.

On the other hand, mothers tend to have much greater contact with their children, increasing the opportunities for violent outbursts directed against their sons or daughters. To whatever extent infanticide is precipitated by the stresses and strains of child rearing, one might expect mothers to outnumber fathers as perpetrators of infanticide.

For the families of the eight women or more who were apparently murdered and dumped on Long Island, NY, by a serial killer, it must be some small consolation that the case is finally receiving wide-ranging media attention. The victims, all believed to have worked as prostitutes, disappeared months or even years ago. But only after the remains of four bodies were discovered in December and an additional four more recently did word of a likely serial killer become a page one story.

This is a familiar scenario to those, like me, who pay attention to such crimes. Serial murders of prostitutes have been tracked in virtually every part of the nation, with many of the cases unsolved and frustratingly cold.

For a number of reasons, prostitutes are the most frequent victims targeted by serial murderers. Foremost is their easy accessibility to these predators. A sexual sadist can hunt the streets of the city or browse the ads on Craigslist, seeking out an available woman (and sometimes the man), looking selectively for the one who he finds most appealing, the one who can best satisfy his violent fantasies. And for money or drugs, the unfortunate prostitute will willingly participate in making his dream a reality, until it becomes too late to escape.

From the killer's perspective, it is also psychologically easier to prey upon those he devalues. Seeing them as "sex machines," programmed to please, he feels little hesitancy or remorse. By dehumanizing his victims, he is killing someone that he views as beneath humanity.

Most important, however, is that the killer who victimizes prostitutes can count on a slow response from law enforcement and minimal attention from the general public. Were he to abduct and kill some middle-class co-ed, the police response would be intense and immediate. But the disappearance of a known prostitute is not necessarily considered foul play, at least not until the remains of several victims are discovered in a remote dump site.

There are times when online editions of newspapers deny readers the curious juxtapositions of stories found in print, unintended though they may be, that occasionally identify fascinating ironies in politics, current events or the social world. For example, an article about on sex education in schools may inadvertently be placed side-by-side with one about the struggles of some single mother somewhere. Or, a photograph of a public servant charged with taking bribes may be coincidentally situated above a story about a newly-discover Ponzi scheme.

In yesterday’s Sunday Globe, the print edition that is, a skillful and lengthy examination of efforts over the years to improve parole prediction tools culminates on page K4 of the Ideas section, just above a small snippet about the limitations on using minor league pitching performance to predict major league success on the mound. In both settings—predicting future criminality and future earned-run-averages—the past is a useful, but rather flawed, indicator of the future.

The most challenging problem in either case is the inherent difficulty in predicting rare events. It is a statistical fact of life that unusual or extreme outcomes can never be reliably anticipated, no matter how sophisticated the prediction device or how voluminous the data used to craft it.

Maria Cramer’s examination of the implausibly low hate crime figures for Massachusetts communities highlights a pervasive and systematic problem in measuring acts of violence and vandalism motivated by bias and intolerance related to race, ethnicity, religion, gender, sexual orientation or disability. However, the troubling portrayal of undercounting reflects only half the story. The reporting problems in Massachusetts may be bad, but they are far worse elsewhere.

Cramer focused almost exclusively on differences in hate crime reporting among cities and towns in the Commonwealth of Massachusetts. Yet, even with the apparent lack of compliance among many jurisdictions statewide, Massachusetts still ranks high among the states around the country -- 9th highest nationally in terms of reported hate crimes per 100,000 population. In 2009, the rate for Massachusetts (5.05) was more than twice the national average (2.37). This, of course, begs the question: how badly would our state rank if the reporting levels were more consistent with reality?

Ever since the awful days of violence and disorder prompted by forced busing in order to desegregate city schools, Boston has struggled to shed its ugly reputation for racism. And, although our state has been singularly progressive in recognizing same-sex marriage, the potential for backlash always exists when breaking down barriers.

Before jumping to conclusions, consider where some other states rank nationally. The three states that sit at the very bottom, with the lowest reported rates of hate crime, are Georgia, Mississippi, and Alabama! This fact alone suggests that the FBI’s hate crime report, mandated by Congressional act in 1990, may not worth the cyberspace in which it resides.

Comparing the official police reports to estimates from victim surveys further illustrates how unreliable hate crime measurement can be. According to the Bureau of Justice Statistics, almost 200,000 Americans are victimized annually by hate crimes, of which nearly half are reported to the police. Yet, according to the FBI, the number of incidents submitted by law enforcement around the country is less than 10,000 annually. Although the victimization counts are likely inflated (as some victims may falsely impute bias motivation), the FBI hate crime reports are clearly suspect. At best, they may be used to track trends for a particular jurisdiction; but even then, changes in investigative practices can significantly alter the figures.

“No news is good news,” they say. But when it comes to media coverage of crime figures, it is more that “bad news is big news.” This explains why a modestly cautionary alert about local rates of violence was so prominently featured in recent headlines tied to a mostly positive report on trends in health indicators.

Earlier this week, the Massachusetts Health Council released its biennial compendium on heath, "Common Health in the Commonwealth: Massachusetts Trends in the Preventable Determinants of Health," which includes statistics on everything from tobacco use to obesity, and from asthma to violence. The authors of the report, drawing upon FBI crime counts, note that Massachusetts has the unenviable distinction of leading all states in the Northeast in the rate of violent crime: "At a rate of 457 violent crimes per 100,000 population, the Commonwealth was once again, as in multiple previous years, statistically the most violent state in the Northeast region (comprised on the six New England States plus NY, NJ, and PA)."

Almost in lockstep, the local press relayed this disturbing conclusion about a perilous state of affairs. The Globe tagged its coverage with the headline, “Mass. still leads Northeast in violent crime, survey shows.” In the Herald, the headline read “Report: Massachusetts most violent state in Northeast,” Meanwhile, the Patriot Ledger emphasized a similar theme, “Report: State no. 1 in Northeast for violent crime.”

And the concern over violent crime rates wasn’t limited to the local papers. For example, NECN announced, “Massachusetts is most violent of nine Northeast states,” contextualizing its story with video of recent murder cases.

Despite the remarkable consistency in press coverage, the fact is that Massachusetts’ top-ranking on violence isn’t exactly accurate, at least in terms of suggesting that we are more at-risk than residents of other states in the region.

The recent spike in violence, including today’s massacres in Mattapan, is not cause for alarm, although a healthy dose of concern would certainly be in order. Of course, each life—young and old—sacrificed to the scourge of gang and gun violence is tragic in itself. Still, the death toll is hardly close to the “bad old days” of the early 1990s when the Boston homicide tally topped 150.

To some extent, this year’s rate of murder constitutes an uptick only because of the relative calm of the past couple of years. There are natural and random fluctuations in annual crime rates: What goes up generally comes down, and what goes down generally rebounds.

Notwithstanding the statistical backdrop, the recent spate of gun violence should not come as a surprise. The welcome news from the FBI about the large decline in crime last year overlooks a grim reality for many Americans. Violent crime may be down overall, but not for some segments of the population and in some neighborhood of urban America. In communities like Mattapan, Dorchester and Roxbury, as in sections of Baltimore, Detroit and many other cities, the downturn in crime seems like an illusion. Actually, it is trend happening in other people’s neighborhoods.