Traffic Tech #209: Examining DWI Conviction Rate Procedures |
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EXAMINING DWI CONVICTION RATE PROCEDURES
What is the DWI conviction rate in your home town? It sounds like an easy question -- you just need to know the number of convictions and then divide this number by the number of DWI arrests, right? In fact, this question is often impossible to answer for some jurisdictions and, in practice, the calculations vary from place to place. Often, reported conviction rates are based on a subset of DWI arrests, or convictions for other lesser offenses. Thus, what is reported as the DWI conviction rate in one jurisdiction may be based on an entirely different calculation than another jurisdiction's rate, and the two rates cannot be compared to each other.
Mid-America Research Institute recently completed a project for the National Highway Traffic Safety Administration (NHTSA) to examine how various jurisdictions across the country compute their DWI conviction rates. The objective was to determine if different formulas are used, rather than to compare the actual rates between sites.
The researchers obtained arrest and conviction data from ten sites from across the country, both large and small, urban and rural. They also spoke with local officials about how they compute their conviction rates. What they learned is that there are many factors involved in the DWI conviction process, and several different ways that agencies use to compute their rates.
Factors that Affect Process
The DWI conviction process can be affected by plea bargains, speedy trial laws, offenders who fail to appear (FTAs), and pre-trial diversion practices. Additionally, depending on the number of agencies involved, the data may be recorded in separate databases or in different formats.
Math Makes a Difference
When asked for their DWI conviction rate, most of the participating sites quoted it as a percentage of total DWI dispositions in some time period, usually a year. This does not take into account, however, the number of cases that are not disposed -- for example, those cases where the offender never appears for trial. In some locations, this can be a significant number, and if these cases were included in the calculation, the conviction rate would be much lower.
One site used the ratio of convictions in one calendar year to arrests in that year. Since it can take a year or more to close a case, this kind of calculation actually reports some convictions that related to arrests made in a previous year. Other sites used tracking data, and thus could provide a rate equal to the percentage of a cohort of DWI arrestees that ultimately were convicted of DWI.
Although it would seem that a statewide, complex system would be necessary to provide all the data required to provide a conviction rate that reflects the entire system, the smallest site included in the study showed that, with cooperation from all the organizations involved, an effective system can be set up in any jurisdiction.
Rate Varies by Agency
The type of conviction rate quoted was largely a function of the type of agency doing the quoting and the data available to that agency. Law enforcement agencies were more likely to quote rates based on arrests, while prosecutors and court administrators were more likely to quote rates based on total dispositions. Both types of agencies reported the data they had.
Sensitive Information
Several persons interviewed in the study pointed out that conviction rate information is highly sensitive, and expressed concern that it could be misinter-preted or used for political purposes. For this reason, there is a general reluctance to quote conviction rates, many agencies do not calculate conviction rates, or if they do, the information is not released publicly. Many jurisdictions are hesitant to base their rates on arrests (which includes FTAs) since these rates are lower than rates calculated on total dispositions. This is especially true in jurisdictions with high numbers of FTAs, where conviction rates are beyond the control of the prosecutor.
Case Studies
The report presents case studies of each of the ten participating jurisdictions' adjudication systems and the circumstances relevant to how they determine their conviction rates. It also includes the jurisdictions' reported conviction rates where available, and for some cases, the rate when using alternative calculation formulas.
Recommendations
When requesting DWI conviction rates, specify both the numerator and denominator, and ask for the raw numbers and the time periods, in addition to the calculated result.
Consider the true conviction rate to be the number of DWI convictions resulting from, and divided by, the number of DWI arrests in a given time frame. FTAs would not be counted as convictions. Plea bargains might be counted as convictions if a jurisdiction has more than one level of DWI offense and it is common practice to reduce the charge to the lower level.
Jurisdictions and agencies should be encouraged to keep detailed records on the disposition of DWI arrests so that meaningful and consistent DWI conviction rates may be developed, published, and compared. Statewide case tracking systems using information from a uniform traffic citation should be encouraged as a means for maintaining such records.
How to Order
For a copy of Examination of DWI Conviction Rates (55 pages) write to the Office of Research and Traffic Records, NHTSA, NTS-31, 400 Seventh Street, S.W., Washington, DC, 20590, or send a fax to (202) 366-7096. Amy Berning was the contract manager for this project.
U.S. Department
of Transportation
National Highway
Traffic Safety
Administration
400 Seventh Street, S.W. NTS-31
Washington, DC 20590
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If you would like to receive a copy contact:
Linda Cosgrove, Ph.D., Editor, Evaluation Staff
Traffic Safety Programs
(202) 366-2759, fax (202) 366-7096
mailto:lcosgrove@nhtsa.dot.gov