TESTS OF NONLINEAR DYNAMICS IN U.S. HOMICIDE TIME SERIES,AND THEIR IMPLICATIONS*

Attempts to explain temporal patterns in U.S. homicide data usually assume that a linear process accounts for the variation. A nonlinear process is an obvious alternative, however, and reasonable arguments suggest that nonlinearity may in part underlie homicide series dynamics. This paper applies tests for nonlinearity to national time series of homicide rates and counts. The results provide relatively little evidence of nonlinear structure; instead, a linear (random walk) process appears to generate most of the change in the series. Although this supports the unstated assumptions of current theories, it also raises questions about why homicides should follow a linear time path in the first place.     

The Impact of the 1994 Federal Assault Weapon Ban on Gun Violence Outcomes: An Assessment of Multiple Outcome Measures and Some Lessons for Policy Evaluation

The Federal Violent Crime Control and Law Enforcement Act of 1994 bans a group of military-style semiautomatic firearms (i.e., assault weapons) and ammunition magazines capable of holding more than 10 rounds. Ban advocates argue that these weapons are particularly dangerous because they facilitate the rapid firing of high numbers of shots. Though the banned guns and magazines were used in only a modest fraction of gun crimes before the law, it was hypothesized that a decrease in their use might reduce gunshot victimizations, particularly those involving multiple wounds and/or victims. In response to a Congressional mandate for an impact assessment of the law, this study utilized national and local data sources and a variety of analytical techniques to examine the ban's short-term impact on gun violence. The ban may have contributed to a reduction in gun homicides, but a statistical power analysis of our model indicated that any likely impact from the ban will be very difficult to detect statistically for several more years. We found no evidence of reductions in multiple-victim gun homicides or multiple-gunshot wound victimizations. The findings should be treated cautiously due to the methodological difficulties of making a short-term assessment of the ban and because the ban's long-term effects could differ from the short-term impacts revealed by this study.     

美国命案状况及趋势分析

以美国联邦调查局“统一犯罪报告”中的命案统计数据为依据，介绍并分析了美国命案的发案及破案的最新状况和趋势，并对命案的某些重要特征进行了必要的分析。分析结果显示，同我国的“命案必破”相比，美国近些年来的命案发案率和命案侦破率均出现了下降的趋势。     

命案中关系人作案判定依据之探讨

关系人作案的命案在犯罪现场的特殊性、调查走访信息的矛盾性、案后表现与侦查询问中的反常性以及现场证据的印证性等，都有别于一般的杀人案件。虽然这些特点并非使得关系人作案与其他一般杀人案件泾渭分明，或具有永久性法则般的稳固性，却也为侦查人员在命案侦查中把关系人作案作为一种优先考虑提供现实依据。     

THE SHORT‐TERM EFFECTS OF EXECUTIONS ON HOMICIDES: DETERRENCE,DISPLACEMENT, OR BOTH?*

Does the death penalty save lives? In recent years, a new round of research has been using annual time‐series panel data from the 50 U.S. states for 25 or so years from the 1970s to the late 1990s that claims to find many lives saved through reductions in subsequent homicide rates after executions. This research, in turn, has produced a round of critiques, which concludes that these findings are not robust enough to model even small changes in specifications that yield dramatically different results. A principal reason for this sensitivity of the findings is that few state‐years exist (about 1 percent of all state‐years) in which six or more executions have occurred. To provide a different perspective, we focus on Texas, a state that has used the death penalty with sufficient frequency to make possible relatively stable estimates of the homicide response to executions. In addition, we narrow the observation intervals for recording executions and homicides from the annual calendar year to monthly intervals. Based on time‐series analyses and independent‐validation tests, our best‐fitting model shows that, from January 1994 through December 2005, evidence exists of modest, short‐term reductions in homicides in Texas in the first and fourth months that follow an execution—about 2.5 fewer homicides total. Another model suggests, however, that in addition to homicide reductions, some displacement of homicides may be possible from one month to another in the months after an execution, which reduces the total reduction in homicides after an execution to about .5 during a 12‐month period. Implications for additional research and the need for future analysis and replication are discussed.