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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

 

Reports Page

 

ICD Page   Improving Crime Data Project

 

March 16, 2009

Technical Details: How the City Homicide Rates Were Adjusted

The statistical model used to estimate adjusted homicide rates for the 63 large US cities was specified as follows:

Homrate = a + b1(Poverty) + b2(MdInc) +  b3(MaleUnem) + b4(Black) +  b5(FemHead), where

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Homrate = Homicides per 100,000 city residents;

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Poverty = Percentage of families with incomes below the poverty line;

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MdInc = Median household income;

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MaleUnem = Percentage of males age 20-64 unemployed;

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Black = Percentage of the population black; and

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FemHead = Percentage of families with children under the age of 18 headed by a female.

The homicide data are from the FBI’s 2007 Uniform Crime Report.  The socio-economic indicators are from the American Community Survey of the US Census Bureau.

The model was estimated using ordinary least squares regression on the 2005-2007 average homicide rates and socio-economic indicators for the 63 cities. The parameter estimates from this model were then applied to the 2007 homicide rates. The model explains about 71% of the variation in homicide rates across the cities.

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 63 cities arrayed by the unadjusted and by the adjusted rankings; see Table-2 for an alphabetical listing of the cities.

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