Planning to Evaluate a Crime Prevention Through Environmental Design Strategy? What Are Some Challenges?

Experimental designs are more difficult to conduct with CPTED strategies.
Many CPTED studies have been conducted to determine the impact of the strategies on specific geographic areas. Experimental designs are more challenging because random assignment is more difficult to accomplish when the units of measurement are areas instead of individuals, it is often difficult to identify comparable areas to serve as controls, and it can be challenging to ensure that the intervention does not inadvertently affect the control area. Use of statistical techniques to control for other variables that might be influencing outcomes will help increase the scientific rigor of the evaluations.

Environmental factors require longer data collection periods.
Although research shows that fear of crime and perceptions of safety are impacted by time of year, many of the CPTED studies have had short follow-up periods which do not account for seasonal variations. Longer follow-up periods would ensure comparison periods are accurately matched by time of year to decrease the chance that fluctuations in factors such as temperature or hours of daylight are responsible for observed outcomes. In addition, studies of CPTED strategies like street lighting or outdoor cameras should take into account environmental factors such as time of day since these types of strategies may have different effects on different types of crime depending on whether it's day or night. Use of statistical techniques to control for other variables that might be influencing outcomes will help increase the scientific rigor of the evaluations.

Multiple CPTED strategies are often implemented together making it harder to determine which individual components of the various strategies are responsible for reductions in crime and why.
A CPTED strategy is implemented to address the ability and opportunity of a criminal to offend. Lack of pre-planning may result in several strategies being used when only one strategy may be needed. Proper planning before implementing CPTED principles will help insure that only the strategies that are most needed or most likely to directly address the problem will be implemented. Different CPTED strategies implemented around the same time in a community will increase the difficulty of isolating the specific program components responsible for the outcomes if the strategies are not properly documented. Other events/factors that could be viewed as alternative explanations must also be documented and then ruled out before impact can be attributed to use of CPTED.

Accounting for implementation successes and failures will be difficult when program implementation data is incomplete.
In many instances, when CPTED strategies are implemented, the process of collecting data that would show why and how a CPTED strategy was implemented has been overlooked in favor of collecting outcome data to show its impact. However, it will be difficult to determine potential reasons for program success or failure if implementation has not been properly documented. In addition, data indicating why a particular strategy was chosen and how it was implemented will provide information on how these factors affected program outcomes.

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