Study
Cook and MacDonald (2011) used a quasi-experimental design to assess the impact of BIDs in Los Angeles on crime rates and provide a cost–benefit analysis. In this study, using a fixed effects regression approach, yearly counts of crime and arrests for the city of Los Angeles as recorded by the police—aggregated to the police reporting district level—were modeled against membership of the treatment group or the remainder of reporting districts in Los Angeles. There were 1,072 police reporting districts in this study. Data was analyzed for the period 1995–2004. The analysis primarily dealt with robbery, assault, burglary, and auto theft, as these crimes are more likely to occur in public settings.
The study analyzed data on 30 BIDs; these were reported to cover 179 police reporting districts. The unit of analysis was the count of crime in the reporting districts per year. As data for 12 years was analyzed, there was a total of 2,148 observations for the treatment areas. All reporting districts that did not contain a BID comprised the comparison group; there were 893 such reporting districts. For these areas, there was a total of 10,716 (893 districts x 12 years) observations over the 12-year interval. A fixed effects model was used to estimate the influence of unmeasured variables, but the comparison group was not formed in such a way as to ensure equivalence with the treatment group.
The authors conducted a dose-response (and other) analysis to test the issue of causality; the results support the interpretation that observed effects may be attributed to the intervention. The length of the evaluation period varied depending on when the BID was formed, and varied from 3 to 8 years.
Study
Brooks (2008) used a quasi-experimental design to assess the impact of Business Improvement Districts (BIDs) in Los Angeles, Calif., on crime rates. In this study, using a fixed effects regression approach, yearly counts of crime and arrests for Los Angeles as recorded by the police—aggregated to the police reporting district level—were modeled against membership of the treatment group or control. Different regression models were tested, using a series of control groups to examine the robustness of the study outcomes. These control groups were defined in different ways, so that:
- Treatment groups were compared to all other police reporting districts, of which there were a total of 1,009.
- Treatment groups were compared to those areas that nearly formed a BID (that is, they began the process but did not complete it).
- Treatment groups were compared to those police reporting districts that were contiguous to BIDS.
- Finally, control groups were identified—using propensity score matching—as areas that would have a similar demand for BIDs as the actual BID areas, based upon a range of pre–BID characteristics that included levels of crime, physical layout, and sociodemographic variables, as measured by the Census.
For the CrimeSolutions review of this study, the focus was on the outcomes that compared the BIDs treatment areas with control groups identified through propensity score matching. There were 30 BIDs, comprising 124 police reporting districts. In the regression model, the unit of analysis was the count of crime per year for each reporting district. Data was available for the period 1990–2002. For the entire interval, there were 1,612 observations at the reporting district level for the treatment group (620 before and 992 after intervention). The number of observations ranged from 1,716 (the comparison with those police reporting districts that were located in areas that were almost BIDs) to 11,505 (the comparison with all reporting districts.)
The units of observation were not aggregated to the periods before and after intervention, or for a long series of time periods, but were instead aggregated for each of the yearly intervals between 1990 and 2002. Thus, the observations were for each police reporting district for each year for which data was available. The length of the evaluation period varied, depending on when the BID was formed, from 1 to 8 years.