Maybe I Should Do This Alone: A Comparison of Solo and Co-offending Robbery Outcomes

Abstract

There has been a notable increase in co-offending research in recent years, with most studies focusing on the causes and correlates of co-offending. There is little known, however, about the consequences of co-offending and how it may influence crime event outcomes for the offender. The present study compares the monetary reward and arrest risk of solo and co-offending robberies. Data from the National Incident Based Reporting System were analyzed to examine the characteristics and outcomes of robberies perpetrated by one, two, three, and four or more offenders. Though co-offending incidents were associated with greater total property value stolen, co-offending incidents resulted in significantly less property value per offender, controlling for other incident characteristics. The likelihood of an incident resulting in an arrest significantly increased with the number of offenders. We discuss the implications of our findings for theory and research on the real and perceived benefits and costs of co-offending.

Keywords:

• co-offending
• robbery
• NIBRS
• accomplices

Acknowledgement

We would like to thank four anonymous reviewers for their helpful comments on an earlier draft of this paper.

Notes

¹ Weerman’s (2003) description of the exchange of goods between co-offenders highlights that such goods can include money, goods, information, social rewards, etc. That being said, Weerman (2003) notes that for more instrumental crimes such as robbery, co-offenders typically provide services in exchange for tangible valuables, such as money and/or goods.

² Bernasco’s (2006) findings from residential burglars in The Hague also challenge the hypothesis that co-offenders allow for the selection of more lucrative and challenging targets. Bernasco (2006) reports there were no significant differences between the target areas of co-offending and solitary burglars with respective to affluence, physical accessibility, social disorganization, proximity to home neighborhood, proximity to city center, or number of properties.

³ We also conducted the subsequent analyses using NIBRS data from 2006. There were no substantive differences with respect to the relationships between co-offending and dependent variables of interest, thus increasing our confidence that the results reported herein are not unique to the 2011 NIBRS data.

⁴ We excluded robbery-homicides from the present study for a couple reasons. First, the accuracy of the criminal earnings resulting from fatal robberies is questionable, given that the victim is deceased and cannot report the property loss. Second, NIBRS does not allow us to distinguish between (1) incidents that were initiated as robberies with material gain as the primary motivation and fatal injury to the victim as a secondary offense, and (2) incidents that were initiated as homicides (or assaults that escalated to homicides) with victim harm as the primary motivation and robbery as a secondary offense that resulted from the situational opportunity provided by the homicide. We believe these types of crimes may be substantively different, including the role that co-offenders play. For these reasons, we limit our analyses to non-fatal robberies.

⁵ For example, several victim variables were examined based on previous studies that have linked the use of violence to victim compliance and its potential impact on rewards gained or likelihood of apprehension (e.g. Felson, 2003; Roberts, 2008; Wright & Decker, 1997). Additional research suggests that victim compliance varies by victim characteristics (Schnebly, 2002).

⁶ Other race/ethnicity includes victims who identified as Asian or American Indian.

⁷ NIBRS includes a category for an “unknown” relationship between the victim and offender, as well as a “missing” category. Messner, McHugh, and Felson (2004) have argued that the missing category likely includes incidents in which the police failed to provide any entry because there was no known relationship. Similar to Messner, McHugh, and Felson (2004), we have recoded these missing cases as unknown relationships to avoid omitting cases from the analyses due to missing values. A similar procedure was followed for the offender(s) under the influence variable. If the victim(s), offender(s), and/or police reported that one or more offenders were under the influence of drugs or alcohol, the incident was coded as 1. A value of 0 indicates a negative response or no response.

⁸ Other race/ethnicity includes offenders who identified as Asian or American Indian.

⁹ Note that NIBRS does not collect data on offender ethnicity.

¹⁰ Many of the variables did not meet the assumptions of the parametric ANOVA test. Therefore, the non-parametric Kruskal–Wallis ANOVA was used for the following variables: total property value, property value per offender, any arrest, arrest per offender, number of victims, age of victim(s), female victim(s), male and female victims, Hispanic victim(s), other race/ethnicity victim(s), multiple race/ethnicity victim(s), offender(s) known to the victim(s), offender(s) under the influence, private location, and semi-public location.

¹¹ We also conducted pairwise comparisons to examine how the mean values of the independent variables vary by the number of offenders. In the interest of parsimony, we do not report these additional 108 significance tests, though they are available from the authors upon request. We do note in the text when the pairwise tests with respect to solo vs. co-offending incidents differ from the ANOVA findings reported in Table 3.

¹² As Morselli and Tremblay (2004) argue, this method is preferred over alternatives, such as deleting extreme values, for a number of reasons. It normalizes the distribution, reduces extreme values without removing them from the analysis, and retains the proportional scale. In their study of criminal earnings, Morselli and Tremblay (2004) report that 10.3% of respondents earned less than one dollar in money-oriented crimes; these cases were each assigned one dollar so they could remain in the logged transformation, at which point the values were transformed back to zero. We found similar percentages of robberies resulting in less than one dollar (12.7% for robberies committed by one offender, 11.2% for those committed by two offenders, 11.1% for those committed by three offenders, and 10.3% for those committed by four or more offenders). These cases were assigned a value of one dollar so they could remain in our logged transformation, at which point they were transformed back to zero.

¹³ These results are available upon request from the authors.

Additional information

Notes on contributors

Marie Skubak Tillyer

Marie Skubak Tillyer is an assistant professor of criminal justice at the University of Texas at San Antonio. Her research interests include violence, victimization, and crime prevention. Her recent research has appeared in Crime and Delinquency, Justice Quarterly, and Journal of Research in Crime and Delinquency.

Rob Tillyer

Rob Tillyer is an associate professor of criminal justice at the University of Texas at San Antonio. His research interests include decision-making within the criminal justice system, crime prevention, and victimology. His recent journal articles have appeared in Justice Quarterly, Criminal Justice and Behavior, and Crime and Delinquency.