Offering a unifying theoretical perspective not readily available in any other text, this innovative guide to econometrics uses simple geometrical arguments to develop students' intuitive understanding of basic and advanced topics, emphasizing throughout the practical applications of modern theory and nonlinear techniques of estimation. One theme of the text is the use of artificial regressions for estimation, reference, and specification testing of nonlinear models, including diagnostic tests for parameter constancy, serial correlation, heteroscedasticity, and other types of mis-specification. Explaining how estimates can be obtained and tests can be carried out, the authors go beyond a mere algebraic description to one that can be easily translated into the commands of a standard econometric software package. Covering an unprecedented range of problems with a consistent emphasis on those that arise in applied work, this accessible and coherent guide to the most vital topics in econometrics today is indispensable for advanced students of econometrics and students of statistics interested in regression and related topics. It will also suit practising econometricians who want to update their skills. Flexibly designed to accommodate a variety of course levels, it offers both complete coverage of the basic material and separate chapters on areas of specialized interest.

Estimation and Inference in Econometrics

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Preventing Crime: What Works, What Doesn't, What's Promising. Research in Brief. National Institute of Justice.

Crime fell sharply in the United States in the 1990s, in all categories of crime and all parts of the nation. Homicide rates plunged 43 percent from the peak in 1991 to 2001, reaching the lowest levels in 35 years. The Federal Bureau of Investigation’ s (FBI) violent and property crime indexes fell 34 and 29 percent, respectively, over that same period. These declines occurred essentially without warning: leading experts were predicting an explosion in crime in the early and mid-1990s, precisely the point when crime rates began to plunge. Although experts failed to anticipate the decline, there has been no shortage of hypotheses to explain the drop in crime after the fact. Table 1 presents a tally of a Lexis-Nexis search of the most frequently cited reasons for the crime decline in articles in major newspapers over the period 1991‐ 2001. The single most frequent explanation given is the innovative policing strategies put into place. The crime decline is also frequently attributed to increased imprisonment, changes in the market for crack cocaine, the aging of the population, tougher gun control laws, the strong economy and increases in the number of police. In this paper, I attempt to sort out why crime declined in the 1990s. I begin with a review of the facts. I then analyze the leading explanations for why crime fell, looking at possible determinants that changed in some substantial way in the 1990s. Most of the supposed explanations listed in Table 1 actually played little direct role in the crime decline, including the strong economy of the 1990s, changing demographics, better policing strategies, gun control laws, concealed weapons laws and increased use of the death penalty. Four factors, however, can account for virtually

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Understanding Why Crime Fell in the 1990s: Four Factors that Explain the Decline and Six that Do Not

In 1996, a Federal law required the U.S. Attorney General to provide Congress with an independent review of the Many crime prevention programs work. Others don’t. Most programs have not yet been evaluated with enough scientific evidence to draw conclusions. Enough evidence is available, however, to create provisional lists of what works, what doesn’t, and what’s promising. Those lists will grow more quickly if the Nation invests more resources in scientific evaluations to hold all crime prevention programs accountable for their results. Issues and Findings

Preventing Crime: What Works, What Doesn't, What's Promising

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The growth of incarceration in the United States: exploring causes and consequences

Research on the relationship between police and crime, like many criminological topics, is subject to uncertain causal direction and omitted controls. We recommend procedures that mitigate these problems: the Granger causality test, proxies for missing variables, robustness checks, and making data available to other researchers. Because specification problems are common in the social sciences, this strategy has applicability beyond the issue of police and crime. We analyze yearly police data and UCR crime rates, at the state and city levels, pooled over two decades. We find Granger causation in both directions. The impact of crime on the number of police is slight, but the impact of police on most crime types is substantial. The latter result is more robust at the city level.

Specification problems, police levels, and crime rates*

The impact of state prison populations on crime is typically estimated by applying the lambda, the individual crime rate, of prisoners or arrestees. We outline the problems with this approach, attempt to reanalyze the widely divergent lambdas derived in past research, and make adjustments necessary to use lambdas for estimating the incapacitation impact. The result is an uncertain estimate of 16 to 25 index crimes averted per year per each additional prisoner. We argue that regression analysis can provide a better estimate of the impact of prison population growth. Applying the Granger test to pooled state data over 19 years, we found that prison population growth leads to lower crime rates but that crime rate changes have little or no short-term impact on prison population growth. Next we regressed crime rates on prison population and conclude that, on average, at least 17 index crimes are averted per additional prisoner. The impact is limited mainly to property crime.

Prison population growth and crime reduction

Three‐strikes laws provide very long prison terms for certain criminals with prior convictions of serious violent crimes. It is likely that the laws increase homicides because a few criminals, fearing the enhanced penalties, murder victims and witnesses to limit resistance and identification. With a state‐level multiple‐time‐series design, we find that the laws are associated with 10–12 percent more homicides in the short run and 23–29 percent in the long run. The impact occurs in almost all 24 states with three‐strikes laws. Furthermore, there is little evidence that the laws have any compensating crime reduction impact through deterrence or incapacitation.

The Lethal Effects of Three‐Strikes Laws

Research Summary:
The heavy reliance on the use of incarceration in an attempt to address the crime problem has resulted in a dramatic growth in the number of state prisoners over the past 30 years In recent years, however, a growing concern has developed about the impact that large numbers of offenders released from prison will have on crime rates Using a state panel data set for 46 states from 1974 to 2002, this study demonstrates that although prison population growth seems to be associated with statistically significant decreases in crime rates, increases in the number of prisoners released from prison seem to be significantly associated with increases in crime Because we control for changes in prison population levels, we attribute the apparent positive influences on crime that seem to follow prison releases to the criminogenic effects of prison

Policy Implications:
Policy makers should continue to serve the public interest by carefully considering policies that are designed to reduce incarceration rates and thus assuage the criminogenic effects of prison These policies may include changes in sentencing, changes in probation and/or parole practices, or better funding of reentry services prerelease and postrelease

The criminogenic effects of imprisonment: evidence from state panel data, 1974–2002

We estimate the impact of determinate sentencing laws (DSLs) on prison commitments, prison populations, and Uniform Crime Report crime rates. Ten states enacted these laws between 1976 and 1984; all abolished parole and most established presumptive sentences. The research uses a multiple time-series design that, among other benefits, controls for national trends and facilitates the use of control variables. We found that DSLs are clearly associated with prison population growth in only one state, Indiana, and with major reductions in two, Minnesota and Washington. The remaining laws show no evidence of increasing populations and may have reduced them somewhat. The estimated impacts on commitments are similarly varied. There is little or no evidence that DSLs affect crime. Earlier studies evaluating individual DSLs are often criticized for poor research designs, and our findings support the criticisms.

Thomas B. Marvell

Papers

Specification problems, police levels, and crime rates*

Prison population growth and crime reduction

The Lethal Effects of Three‐Strikes Laws

The criminogenic effects of imprisonment: evidence from state panel data, 1974–2002

Determinate sentencing and abolishing parole: the long‐term impacts on prisons and crime*