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Structural Intervention Time Series Analysis of Crime Rates: The Impact of Sentence Reform in Virginia

AbstractWe adopt a structural time series analysis to investigate the impact of parole abolitionand sentence reform in Virginia on reported crime rates. The Commonwealth of Virginiaabolished parole and reformed sentencing for all felony oﬀences committed on or afterJanuary 1, 1995. To examine the impact of Virginia’s change in legislation on reportedcrime rates from 1995 onwards, we perform an intervention time series analysis basedon structural time series models. We empirically ﬁnd that the change in legislation hassigniﬁcantly reduced the burglary rates and to a lesser extent the murder rates in Virginia.For other violent crimes such as rape and aggravated assault the evidence of a signiﬁcantreduction in crime rates is less evident or is not found. This empirical study for Virginiaalso provides an illustration of how an eﬀective intervention time series analysis can becarried out in crime studies.Keywords: Intervention time series analysis; Crime rates; Structural time series models;Unobserved components time series models.