is clear, however, that some level of adaptation occurs. Curtis and Wendel (1999) and National Development and Research Institutes (1998) have documented the development of delivery and beeper services in New York. National Development and Research Institutes (1998) and Richard Curtis (interview with committee members) have described the use of brokers and other intermediaries. Williams et al. (1989) have documented adaptation through shifting the hours in which drug selling occurs.
Green (1996) studied the extent of geographic displacement of drug dealing in response to the SMART program in Oakland, CA. This program combined increased enforcement of housing and fire codes with traditional tactics, such as arrests and stops at high-activity drug sites. Green found that police contacts with drug dealers decreased within two blocks of 40 percent of the sites and increased within two blocks of only 6 percent of the sites. It is not clear, however, whether this indicates a net decrease in drug dealing activity as a result of the SMART program. It is possible that police contacts decreased because dealers took actions to hide their operations from police while SMART was being carried out. It is also possible that drug sales increased at locations that were separated from the SMART sites by more than two blocks.
In summary, it is clear that drug dealers engage in various forms of adaptive behavior. It is not clear how important this behavior is in counteracting the effects of law enforcement operations. Nor is it clear what, if anything, the police can or should do in response if adaptive behavior does significantly impair the effectiveness of law enforcement.
The basic principle of incapacitation (Blumstein et al., 1978:65) is that if an offender who commits crime at an annual rate of λ is removed from the streets for S years, λ×S crimes are averted. So, for example, if an offender who averages 100 crimes per year is incarcerated for 2 years, one can expect 200 crimes to be averted over the period. Incarceration may also have the added effect of deterring current and potential offenders from committing future crimes.
Of course, no such reductions in crime can be expected if the offender’s crimes are replaced. The likelihood that an imprisoned (or deterred) offender’s crimes will be replaced varies by type of offense. A serial rapist’s crimes almost certainly are not replaced on the street, so one can expect his full array of crimes to be incapacitated. The situation might be quite different for a drug dealer. When drug dealers are imprisoned, their drug transactions may be effectively replaced by some combination of recruiting new sellers or by increasing the rate of activity of sellers