Philadelphia School District officials have touted a 29 percent decline in serious incidents over the last two years.
They promote it in news releases. They promote it on their website. When callers to the district are put on hold, they hear it in a recording.
But this figure deserves a closer look.
The district's assertion is based on a comparison of incidents between the 2007-08 school year and 2009-10. But its math compares raw numbers without accounting for a significant drop in enrollment during that period and an unusual spike in incidents after a highly publicized assault.
The widely accepted standard for measuring crime used for the FBI's Uniform Crime Statistics divides total crime by population to yield a crime rate. Under that method, the district's serious-incident rate dropped 22 percent, from 4.1 incidents per 100 students to 3.2, The Inquirer found.
Perhaps more important, the 2007-08 school year had a significant spike in incidents unmatched in the last decade. The spike came after the principal at a South Philadelphia elementary school failed to report an assault on a student, prompting a district crackdown on reporting.
Incident reports rose about 50 percent daily for several months, said James B. Golden, former district safety chief.
"The principals said: 'You want reporting? We'll give you reporting,' " Golden said.
There were 14,743 incidents - violent and nonviolent - reported that school year, more than any year in the last decade and up 14 percent from the previous year, according to state reports.
The next year, 2008-09, the year Superintendent Arlene C. Ackerman arrived, incident numbers dropped a nearly commensurate 11 percent.
In addition, the district has been shedding students and schools, which automatically drives down its incident numbers.
The district's enrollment has changed dramatically during the last decade. Since 2000, enrollment has dropped by 57,000, to 155,000. Most recently, the district decided to cast off more of its low-performing schools to charter operators. The list includes several troubled neighborhood high schools such as Audenried, Simon Gratz, Olney East, and Olney West. These schools rank among the district's most violent.
The Inquirer also came up with a violence rate for every school. That analysis included all serious incidents excluding drug, alcohol, and fire.
As a group, the neighborhood high schools experienced 17 percent more violent incidents in 2009-10 than they did in 2005-06, according to The Inquirer analysis.
Notably, these high schools account for 84 percent of district schools cited by the state as "persistently dangerous."
Taking a five-year snapshot of serious-incident data smooths over the reporting spike and spans two administrations.
Doing that shows a more modest decline in the serious-incident rate from 3.6 incidents per 100 students to 3.2, or 11 percent.
And that doesn't take into account the teachers, administrators, union officials, and parents who told The Inquirer that schools were not reporting serious incidents, which raises questions about the 11 percent improvement.
But school officials continue to boast of improvement. At a City Council hearing last month, Associate Superintendent Tomás Hanna said serious incidents were down 11 percent over 2009-10 in a year-to-date comparison.
The district declined to provide The Inquirer with numbers to calculate a crime rate for the period.
Numbers aside, the district's violence picture is largely what it was five years ago. Then and now, three out of every 100 students are the victim or perpetrator of violent school crime.
Inquirer staff writers Susan Snyder and John Sullivan contributed to this article.