Crime Rates

Crime rates are standardized measures of crime levels. In mathematical terms, a crime rate can be expressed as (MIN) × K where M is an estimate of the amount of crime occurring in a particular setting during a specified period of time, N is an estimate of the population at risk, and A' is a constant determined by the analyst. So, if for hypothetical Community A, we determine that for the last calendar year, there were 9,300 crimes committed against property, and if the population of Community A is 458,000, the property crime rate per 100,000 for this community for the year in question is calculated as (9,300/458,000) × 100,000 = 2,030.6. Using this general approach, crime rates can be calculated for any size social unit from the neighborhood to the nation-state and for any temporal period.

Unlike raw counts of crimes, rates take the size of the at-risk population into account. Whereas a comparison of the raw or absolute numbers of crimes across communities or within any particular community over time might suggest significant variations, a comparison of crime rates allows the analyst to determine whether the differences are real or merely a function of differences in population size.

Crime rates are useful for a number of reasons. As standardized measures of crime levels, they can serve as useful indicators of the quality of community life. Policy planners utilize crime rate measures to assess the need for social interventions and the relative success of crime control policies. Academic investigators rely on crime rate data as they attempt to investigate the relative value of empirical predictions associated with competing criminological theories.

In a fundamental way, the value of crime rate measures is reliant upon the appropriateness of the estimates of the numerators and denominators used in rate construction. Estimates of the former tend to be derived from one of three sources: the data collected by police, the reports of members of the general public who are asked about their victim experiences in surveys, and the reports of offenders. It has been well established in the research literature that each of these sources of crime data has characteristic flaws. As a result, it is prudent to think of these numerator estimates as somewhat biased samples of all crimes occurring.

The denominators of crime rates also present some formidable problems. Although so-called crude crime rates (like the hypothetical example given in the first paragraph of this entry) offer several advantages over the use of raw numbers, they fail to take account of information regarding the internal structure of the at-risk population. For instance, because most crime is committed by people in early adulthood (ages 18–26), it might make more sense to standardize the rates with reference to the size of this segment of the population rather than with reference to the overall population. Thus, two communities of similar size might differ with respect to their crude crime rates because one is truly more lawless than the other, or because one of the communities might have much more of its population clustered in younger age groups. A comparison of age-specific crime rates would permit an assessment of the value of these two accounts.

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