Contemporary Case Control
The Contemporary Case Control study involves conducting an on-scene investigation of a crash as soon as possible after it occurs. A “go-team” monitors police radios or otherwise gets up-to-the-minute news of any crashes in the area. When a motorcycle crash occurs, the go-team travels to the crash site, interviews the rider involved, and records BACs and other pertinent data. If necessary, the go-team goes to the hospital to collect whatever data could not be collected at the crash site. If all data cannot be collected between the crash site and hospital (e.g., the motorcyclist is fatally injured and doesn’t go to a hospital), the go-team uses whatever means necessary to collect as much of the desired data as possible.
At a later time, the team goes to the crash site and attempts to collect BAC and other data from randomly passing motorcyclists who serve as comparison cases. The comparison cases will ideally be recorded at approximately the same time on the same day of the week, unless that would be inappropriate (e.g., one of the days is a holiday). In some cases, the comparison case will be located as near as possible to the crash site, when safety or other issues prevent using the exact site. The study protocol may call for one or more comparison case for each crash case. Having multiple comparison cases makes it easier to control statistically for differences between comparisons and crash case riders. An informal power analysis was conducted as part of this project, to determine the number of cases that would be necessary to obtain statistically significant results in a Contemporary Case Control study. The analysis indicated that 500 pairs of case and comparison riders (1,000 riders total) should be sufficient (Peck, personal communication, 2002).
Both crash and comparison data can be difficult to obtain. Both require the cooperation of the riders. In the case of the crash-involved rider, the rider may be gone by the time the go-team arrives—if the crash was relatively minor, the rider may have left quickly afterward. This may skew the sample toward more severe crashes. In more serious crashes the rider may go to the hospital, requiring the go-team to determine where the rider has gone and to attempt to get there before the rider is released. Once the rider is contacted, the rider may choose not to cooperate, although in some cases it may be possible to get BAC measurements through the police or the hospital. Comparison-case riders need to be pulled out of the traffic stream. This generally requires the cooperation of police, who conduct the actual traffic stop. Once again, riders may choose not to participate. In the only major Contemporary Case Control study of motorcyclists in the United States, The Motorcycle Accident Cause Factors and Identification of Countermeasures, a.k.a. the “Hurt” Report (1981), cooperation levels of both crashed riders and comparison riders was considered sufficient. Riders may be more inclined to participate if the field interviews are conducted by motorcyclists – a technique that was used in the Hurt study. Comparison cases may be more cooperative if police stops are conducted by motorcycle officers. Evidence indicates that male and female riders may both be more comfortable stopping for female researchers than male researchers. There may also be value in advertising the research project within the motorcycling community and getting the cooperation of motorcycle organization leadership so that riders are prepared for the possibility of stops and less inclined to see motorcyclist-only traffic stops as being unfair. One way to get around the appearance of singling out motorcyclists would be to stop cars as well, although this would increase the cost and complexity of the study with no real value added in the data collected (if any) from car drivers.
Whether a police officer conducts the stop (comparison case) or the researchers attempt it, there may be benefit to advertising the stop in advance by means of a sign or signs upstream from the stop location. Given the fact that the go-team is interviewing riders and visiting the crash scene, there is a possibility of collecting large amounts of useful data (e.g., roadway type, road geometry, first main event, etc.). The more that such data are collected, the more important it becomes that the go-team be trained in crash investigation.
The Organisation for Economic Co-operation and Development (OECD) has created an international methodology for On-Scene In-Depth Motorcycle Accident Investigations that contains information useful to groups wishing to conduct a case control study of motorcycle crashes (OECD, 2001).
Any study of this nature will most likely be subject to Office of Management and Budget (OMB) approval. It will also be necessary to secure the cooperation of local law enforcement agencies and hospitals.
The Case Control study is generally capable of collecting large amounts of high-quality data for each case. Because data come from actual crashes and provide good BAC data, it is possible to generate relative risk ratios for crash involvement. Data come from a range of crash severities, from property damage only (PDO) through injury crashes to fatal crashes, though crashes are limited to those reported to police. This method is not as likely to suffer from the problem that using archival data has, of examining only more serious cases that tend to reflect higher BACs, and of BAC testing being more likely for higher-BAC victims. The comparison data collection at the same site, same time, same day of the week, one or two weeks later, provides a control over many of the factors that could influence BAC in crashing riders.
A great deal of effort goes into the data collection for each case, compared to other methodologies (e.g., the use of archival data). Comparison cases may not be well matched on all pertinent factors (e.g., age, gender, experience). Characteristics of the day in which data are collected may not match either. For example, of two successive Mondays, one might be a holiday, or a payday for one of the riders. Weather may also differ. The crash may have been due in part to roadway characteristics such as construction or debris in the road that is gone a week later so that the crash cases and comparison cases are not equal with respect to crash likelihood. In some situations (e.g., a multilane highway crash) it may be impossible to collect comparison data. It may be difficult to find motorcyclists passing during the time set aside to find the comparison case.
Though this type of study has the potential to provide data from a range of crash severities, they will tend to be skewed toward the more severe injury or fatality crashes, since the less-severe crashes may go unreported or be cleared before the go-team can arrive.
It may be difficult to obtain the cooperation of all necessary parties (e.g., rider, law enforcement, hospital personnel). Law enforcement agencies may have rules governing who can be stopped in traffic (e.g., need probable cause) and traffic stops for research studies may not be allowed under these rules.
It may also be necessary to reimburse police agencies for their participation in helping with the roadside survey portion of this type of study.
Similar case-control studies of automobile drivers have been very costly and time-consuming.