Build your own crime stats online

Do you know the current crime rates in your community? Most people, including cops, don’t. Crime rates are typically a back page item that runs once per year, when the official release of the latest numbers occurs. Unless there is a pronounced change in one direction or the other, it doesn’t get a lot of attention. Still, the crime rate is a useful statistic for comparing the safety of one community over another.

The FBI recently created a web page where you can build your own crime rate tables for any jurisdiction, any year, and any type of crime from all the data that is available. This is a huge improvement over the publications that have been available up until now. Those reports contained the same information, but extracting what you wanted was a real chore.

I used this new tool in a Facebook discussion that followed the shooting of U.S. Representative Giffords and others in Arizona. A participant claimed he had done research showing that Chicago had a lower crime rate than Phoenix. His point was that Chicago has some of the most restrictive firearms laws in the country, and Phoenix has relatively liberal gun laws, therefore more guns = more crime.

I used the “table building tool” on the FBI’s web page to show crimes reported by larger agencies, which is defined as a city over 100,000. From there, three types of tables are available, based on jurisdiction, crime type, and year. In any one table, you can display multiples of two variables and one of the third. I chose multiple jurisdictions (Chicago and Phoenix), multiple variables (different crime types) and a single year (2009, the most recent available).

There was no data listed for the aggregate violent crime rate or for forcible rape in Chicago, but the resulting table did show that Chicago’s rate of murder and non-negligent manslaughter was 16.1 as compared to Phoenix’s 7.6. Robbery was 557.4 vs. 235.2 and aggravated assault was 552.1 vs. 271.0. Phoenix has about half the violent crime of Chicago.

Of course, making an argument as to why one city has more crime than another is not so easily done. Crime generally increases directly with population density and indirectly with average household income. Chicago has a population density of 25,502 people per square mile, and a median household income of $35,283. Phoenix has less than a fifth the population density (4816 people per square mile), but a lower household income ($25,370). What role do gun laws play in this? I have an opinion, but I’ll save that for Facebook.

Those numbers, by the way, came from another web service called ZIPskinny, which condenses U.S. Census and other data and parcels it out by zip code.

Crime rate data are generated by local law enforcement agencies and compiled by the FBI’s Uniform Crime Reports division. The crime rate is the number of crimes per 100,000 population. If your town has 25,000 people and there were three homicides there in 2009, your town’s homicide rate is 12 (100,000/25,000 x3). If there are 250,000 people in your city and there were 30 homicides, the homicide rate would also be 12 (100,000/25,000 x30). Expressing the number this way allows for easy comparison of communities of different populations.

Crimes are broken out by violent crimes (murder and non-negligent manslaughter, forcible rape, robbery, and aggravated assault) and property crimes (burglary, larceny-theft, and motor vehicle theft). All of these together, plus arson, are grouped and called Part I offenses. Part II offenses are other/simple assaults, forgery and counterfeiting, fraud, embezzlement, buying, receiving and possessing stolen property, vandalism, carrying and possession of weapons, prostitution, sex offenses not including rape, drug offenses, gambling, crimes against families and children, DUI, liquor law violations, drunkenness, disorderly conduct, vagrancy, and all other offenses. Data for Part I offenses is more complete (cases cleared, age, sex, race of offenders, etc.) than for Part II, for which only arrest data is collected.

It’s important to remember that crime rate statistics are based on reported crimes. There are always crimes that occur but are never reported. The true level of crime is more accurately estimated from victimization studies, where citizens are surveyed to determine if they have been the victims of crime in the measurement period. This unreported crime, known in criminology as the dark figure, can be as high as ten times the number of reported crimes, especially for Part II offenses.

You may never need this information, but it’s good to know where to get it. You may need to win an argument yourself.

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