Crime (Further Empirical Studies)

• Anderson Mutemererwa, 1 March 2005

Is Capital Punishment a Deterrent to Murder?

• H. Dezhbakhsh, P.H. Rubin & J.M. Shepherd (2003), “Does Capital Punishment Have a Deterrent Effect? New Evidence from Postmoratorium Panel Data”, American Law and economics Review, Vol 5(2), pp344-376.

Background to the Study

• A huge debate about the merits of capital crime in the US. So there are profound policy implications.

• Important question is whether the capital punishment deters murders. Anecdotal evidence from psychologists and criminologists initially found no deterrence.

• Yet studies by economists (Ehrlich, 1975, 1977) found a significant deterrent effect a study which was used by the Solicitor General of the USA in a submission to the US Supreme Court in support of capital punishment.

Background to the Study• Ehrlich’s study spurred a huge interest by

econometricians using his data but different model specifications. Inevitable that different results would ensue.

• Capital crime imposed for different crimes (murder, treason, heresy) throughout history and by different authorities (religious and civil). Most Western civilisations have since abolished the death penalty.

• US an exception. Changed positions in the 1970s, first banning it in 1972 and then reversing this in 1976 (under certain carefully specified conditions). 38 states currently have it. Some that do not have it are debating whether to reinstate it and those that do whether they should abolish it.

Background to the Study• Debate on capital punishment in US involves

moral principles and social welfare considerations. Moral arguments tend to be theoretical while welfare ones are empirical.

• Becker’s (1968) economic model tends to provide the theoretical foundations for much of the empirical work.

• Ehrlich extended Becker’s work; Hence increases in perceived probabilities of apprehension, conviction given apprehension or conviction given conviction will reduce an individual’s incentive to commit murder.

• Changes in legitimate and illegitimate income opportunities have a similar crime-reducing effects.

Research Questions• Statistics show that although executing states

had higher rates of murder than non-executing ones, the rates are converging. Is there a deterrent effect from capital punishment?

• What about certain murders that are not “deterrable” such as non-premeditated crimes of passion and non-negligent manslaughter (see Shepherd (2004))?

• Looked at the functional form of the model bridging the gap between an individual’s behaviour and that of county, state or nation and suggest improvements.

Model Specification• A murder supply equation (macabre as it

may sound!) is specified for a county and denoted by

• Mi,t= αi+β1Pai,t β2Pc|ai,t + β2Pe|c +γ1Zi,t+TDt+εi,t

• The murder supply equation is built from an individual’s decision rule of the following form

• Ψt=f(Pat, Pc|at, Pe|ct, Zt, ut) where Ψt =1 when an individual commits murder during period t and Ψt = 0 otherwise

(Economic) Model of Murder• The above is called the murder supply equation.• The decision (for an individual) whether or not to

commit murder (ψj,t) is a function of the individuals subjective probability (P) conditional on apprehension (a) conviction (c) and execution (e), the individual’s own economic and demographic characteristics (Z) and other random effects (u).

• TD is a time trend dummy which captures national trends such as violent TV programs etc.

• ai is a county-specific fixed effect.• Summing up all individuals in a county and

dividing by the county population allows the calculation of the murder rate for a county, Mi,t.

(Economic) Model of Murder• Added to the murder supply equation will be three

expenditure models for the law enforcement agencies: police, judicial-legal and prisons

• Pai,t=φ1,t+φ2Mi,t+ φ3PEi,t+ φ4TDt+ζi,t

• Pc|ai,t=φ1,t+φ2Mi,t+ φ3JEi,t+ φ4PIi,t + φ5PAi,t +φ6TDt+ζi,t

• Pe|ai,t=φ1,t+φ2Mi,t+ φ3JEi,t+ φ4PIi,t + φ5TDt +ζi,t

• JE is expenditure on judicial and legal system, PE is the police payroll and PI is peer influence such as a Republican candidate’s percentage of state-wide votes whil TD is the same as in the murder supply model.

• If police and prosecutors want to minimise the social costs of crime, they must balance the marginal cost of enforcement with the marginal benefits of prevention. Hence more

Results and Conclusions

• The data came from 3 054 counties for period 1977-96.

• The results of the models reflect strong deterrent effects of execution.

• The execution probability is negative and highly significant. This suggests that the Results and Conclusions perceived probability of execution given that one is sentenced to death leads to a lower murder rate.

• The sentencing effect is weak and does not seem to have a deterrent effect.

Results and Conclusions

• The murder rate appears to increase with aggravated assault and robbery. This suggest that these crimes are partly caused by the same factors which lead to murder. Also, some murders are by-products of robbery and aggravated assaults.

• Demographic effects are also important; a larger percentage of African-Americans (as opposed to other minorities) is associated with higher murder rates while an increase in teenage population appears to lower the murder rates.

Results and Conclusions

• Finally in those counties with a high members of the NRA, the murder rates appears to be high--- high ownership of handguns, leading to guns being the weapons of choice in confrontations.

• Police expenditure has a consistently positive effect on arrestPai,t=φ1,t+φ2Mi,t+ φ3PEi,t+ φ4TDt+ζi,t

• The same is true for the judicial-legal systemPc|ai,t=φ1,t+φ2Mi,t+ φ3JEi,t+ φ4PIi,t + φ5PAi,t +φ6TDt+ζi,t

Pe|ai,t=φ1,t+φ2Mi,t+ φ3JEi,t+ φ4PIi,t + φ5TDt +ζi,t

• Joanna M. Shepherd (2004), “Murders of Passion, Execution Delays, and the Deterrence of Capital Punishment”, Journal of Legal Studies, Vol. 33, pp 283-321.

Research Question?

• Which murders are deterred and what of the effect of a wait on death row on deterrence?

• What types of murders are deterred?

Data and Model

• The data consists of monthly state level data for the period 1977-99.

• During this time 7 416 inmates served on death row and 598 of them were executed.

• The model is specified asM = β1 DETERi,t + β2 ECONi,t +β3 DEMOi,t + β4 si + β5 γt + β6 zt+εi,t

• DETER is a vector of deterrent variables (probability of sentencing to death row and execution)

Model Specification• ECON is a vector of economic variables (real

per capita income and monthly unemployment rate)

• DEMO is a vector of demographic variables; age (specifically the percentage of population which is between 10 and 29 years of age), percentage of population which is African-American, percentage of population which is minority other than African-American.

• γ is a series of year dummies, z is a series of monthly dummies and the s is a series of state dummies (three strikes, non-death penalty for murder)

Results

• Probability of a death row sentence is a deterrent to all types of murder.

• Shorter waits on death row before execution also deter murder– the longer the wait, the higher the murder rate and vice versa (given that the average wait on death row has risen from 1 year in 1981 to 12 years in 1999).

• Probability of execution also deters all murders (by intimates and acquaintances or strangers, murders of white or blacks).

Results and Conclusions

• In addition, the death sentence appears to deter both blacks and whites (in answer to conjecture that the death sentence is racist and disproportionately falls on blacks)

Result and Conclusions• The Shepherd study confirms and extends the

Dezhbakhsh et al study, namely that the death penalty deters crime.

• She also goes further by showing that all murders are deterred by capital punishment and this deterrence cuts across race. Recall that Dezhbakhsh et al had not given an unequivocal answer to this question.

• The key conclusion is that the expected penalty (the probability of arrest, conviction and a lengthy prison sentence/execution) affects the potential criminal’s desire to commit a crime.

Other studies• Look at John R. Lott, Jr., And David B. Mustard

(1997), “Crime, Deterrence, And Right-to-carry Concealed Handguns”, Journal of Legal Studies, vol. XXVI, pp 1-68.

• This study looks at the issue of carrying concealed hand guns as a deterrent to crime across the whole USA.

• The main conclusion is that allowing citizens [who have no history of crime or mental illness] to carry concealed handguns deters violent crime. Makes the claim that, as a result, if the whole USA allowed the carrying of concealed weapons in 1992, 1 414 murders and 4 177 rapes would not have taken place. An estimated social benefit of $5.74 billion would have been realised.

Other studies• However, the study also notes that this

resulted in property crimes involving stealth where the contact between the criminal and the victim is low or no-existent. This is especially in large population areas.

• The study also supports the economic notion of deterrence. High arrests rates (irrespective of eventual conviction) consistently reduce crime rates. The economic reason of which is that increased arrest rates significantly increases the economic penalty on criminals.