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      Improving Crime Data

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Back to: Press Release

 

Table-1: Listing by Unadjusted/Adjusted Scores

Table-2: Listing by Cities

 

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ICD Page   Improving Crime Data Project

 

September 25, 2007

Technical Details: How the City Homicide Rates Were Adjusted

The statistical model used to estimate adjusted homicide rates for the 65 US cities with populations of about 250,000 or more was specified as follows:

Homrate = a + b1(Disadvan), where

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Homrate = Homicides per 100,000 city residents, and

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Disadvan = A factor representing the level of social and economic disadvantage that combines four highly intercorrelated variables (factor loadings in parentheses): the poverty rate (.880), unemployment rate (.717), % black (.889), % female-headed families w/own children under 18 (.938).

The homicide data are from the FBI’s 2006 Uniform Crime Report.  The indicators of socioeconomic disadvantage are from the American Community Survey of the US Census Bureau.

The model was estimated using ordinary least squares regression on the 2004-2006 average homicide rates and disadvantage scores for the 65 cities. The parameter estimates from this model were then applied to the 2006 homicide rates. The model explains about 67% of the variation in homicide rates across the cities. The estimation results are as follows:

Homrate = 13.796 + 8.409(Disadvan)

F1, 63 = 126.03;     p < .001;     R2 = .667;     N = 65

The residuals from this model (the observed homicide rates minus the homicide rates predicted by the model) represent that component of each city’s homicide rate that is not explained by the variables in the model. The adjusted homicide rankings are based on the standardized residuals from the model.

See Table-1 for a list of the 65 cities arrayed by the unadjusted and by the adjusted rankings; see Table-2 for an alphabetical listing of the cities.

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