Section 2


Study Cohorts

A total of 4766 subjects submitted claims for compensation to the SAAQ following whiplash injury in a motor vehicle collision in 1987. Nine of these 4766 individuals were found to have received no compensation or reimbursement of any sort from the SAAQ and were therefore deemed ineligible for inclusion in the study cohort. The remaining 4757 individuals formed the primary source cohort. Of these, 1743 did not have police collision report data entered in the computerized databases and were therefore excluded, leaving a total of 3014 whiplash subjects in the source subcohort aimed at assessing the role of collision-related factors. Reasons for the lack of police report data for 1743 individuals may include the possibility that police may not have been called to the scene of the collision, or that the SAAQ may have been unable to link the police report with the subject's claim for compensation.

The study cohort for the analysis of the duration of absence had 2810 members, since it excluded from the 3014 members the 204 subjects with a recurrence. The study cohort for the analysis of the rate of recurrence had 1666 members, since it excluded from the 3014 members the 1348 subjects with multiple injuries along with whiplash to ensure that the recurrence was related only to the whiplash injury and not to another injury sustained during the collision. The study cohort for the analysis of costs comprised all 4757 members.


Based on the Quebec population figures from 1987 and considering that the 4757 claimants represented the total number of compensated whiplash cases in the province in that year, the annual incidence of compensated whiplash in Quebec in 1987 was 70 per 100 000 inhabitants. The age- and gender-specific incidence rates of whiplash in Quebec in 1987 are shown in Figure 2.1.a. The annual incidence of whiplash among females (86 per 100 000) was more than one and a half times greater than among males (54 per 100 000). This difference in incidence was less marked in the very young and in the older age groups. In fact, for the 5-9 and 65 age groups, the incidence rate of whiplash among males even exceeded the observed rate among females. The highest incidence of whiplash for both genders occurred in the 20-24 age group. For comparative purposes, the age- and gender-specific population-based incidence of all injuries combined that were reported by police in Quebec in 1987 is shown in Figure 2.1.b

The driver-specific annual incidence rate of whiplash, calculated by extrapolating from the data, showed that among those whiplash cases for whom collision-related data were available (3014/4757), the proportion who were driving the vehicle at the time of their injury was 76.3% (2300/3014). Assuming that an equal proportion and distribution of the whiplash subjects with missing collision data were also driving their vehicles at the time of the event, then the total number of whiplash subjects who were drivers was 3613 out of 4757. Therefore, using the total number of licensed drivers in Quebec as the denominator, 99 the driver-specific incidence rate of whiplash in 1987 was 96 per 100 000 licensed drivers per year. Among male and female drivers, the incidence rates were 73 and 126 per 100 000 licensed drivers per year, respectively. The incidence of whiplash can be alternatively expressed in terms of the number of registered motor vehicles rather than in terms of population. Since there were 3.65 million registered vehicles in Quebec in 1987 and 4757 compensated claims for whiplash paid by the SAAQ, there were approximately 131 whiplash injuries per 100 000 vehicles per year in 1987.

Region-specific incidence rates for the 16 administrative regions in the province are shown in Figure 2.2. These rates are based on the region of residence of the whiplash subjects rather than the region in which the collision occurred because the collision location information was frequently unavailable from the computerized databases. The highest incidence rate, 141 per 100 000 inhabitants, was observed in the Lanaudière region, which is located on the north shore of the St. Lawrence River between Montreal and Trois-Rivières. Other regions with high whiplash incidence rates were the Laurentides (112 per 100 000), Laval (97 per 100 000), and Chaudière-Appalaches (91 per 100 000) regions. The lowest incidence rates occurred in the sparsely-populated northern regions of the province: Abitibi-Témiscamingue (47 per 100 000) and Nord-du-Québec/Côte Nord (34 per 100 000). It should be noted that for 2786 out of the 3591 (77.6 %) people for whom the region of residence and the region of the collision were known, the event occurred in the region where the subject resided.

Sociodemographic and Collision-Related Factors

A comparison of the sociodemographic characteristics of the 3014 subcohort members with the 1743 members of the cohort who were excluded because of the lack of collision-related data is provided in Table 1. Table 1 also provides a breakdown of the sociodemographic characteristics according to whether the cohort members sustained only a whiplash injury (n=1666), or other injuries in addition to whiplash (n=1348). Information on employment status was available for only 80% of the study cohort members.

Collision-related information for the study cohort is provided in Table 2, along with a breakdown according to whether the cohort members sustained only a whiplash injury, or other injuries in addition to whiplash. Among the members of the study cohort, only 1.3% were involved in collisions in which at least one person was fatally injured. None of the cohort members died as a result of the motor-vehicle collision. Approximately one-fifth of the cohort members (21.6% or 652/3014) were reported to have been involved in a collision in which there were no injuries apparent when the police were at the scene. For subjects with whiplash only, 27.4% percent of the collisions were recorded as having no injuries apparent at the scene, compared to only 14.5% of collisions in which subjects sustained other injuries in addition to whiplash.

Table 2 also shows the distribution of vehicle types for the whiplash subjects in the study cohort. A large majority (89.5% or 2699/3014) were occupants of passenger cars (including station wagons and four-wheel drive vehicles) or taxis at the time of the collision. Trucks were the second most frequently occupied vehicle type at 5.4%. Less than 4% of the whiplash subjects were using other vehicles, such as buses, motorcycles, mopeds, snowmobiles, and bicycles at the time of the event. Forty-eight (1.6%) of the subjects were pedestrians. Most of the pedestrians (77% or 37/48) sustained other injuries in addition to whiplash in the event, while only 43% of car and taxi occupants sustained multiple injuries. The majority of whiplash subjects (76%) were driving a vehicle at the time of the collision. Most of the whiplash subjects (78.3% or 2361/3014) were involved in events in which a motor vehicle collided with another moving object, usually another motor vehicle. Collisions with other moving objects such as pedestrians, trains, non-motorized vehicles, and animals were rare, accounting for only 3.6% (107/3014) of events. Other types of events included collisions with stationary objects such as lamp posts, guard rails and trees (12.0% or 361/3014) and events not involving collisions, such as roll-overs, submersions and leaving the roadway (8.8% or 265/3014). A total of 707 events (23.5%) that resulted in whiplash injury in 1987 involved only one vehicle, while the remainder were multiple-vehicle events, with the number of vehicles involved ranging from two to ten. The single-vehicle collisions appeared to be among the most severe, as they resulted in a disproportionately high number of whiplash subjects with multiple injuries. Single-vehicle events accounted for 31.2% of whiplash subjects with multiple injuries, compared to only 17.2% of subjects with whiplash only. Of the multiple-vehicle events, 81% (1861/2307) involved two vehicles.

The direction of collision was not recorded very accurately by the police who were called to the scene of the events. For 16 whiplash subjects, the direction of collision was not recorded on the police report. Among those events where something was recorded on the collision report, the direction of collision was coded as indicating an "other" direction of collision, in 34.3%. Thirty-one percent of events were recorded as being rear-end collisions, while 14.5% were head-on collisions. Compared to those who were injured in rear-end collisions, whiplash subjects who were involved in head-on collisions were more likely to have sustained multiple injuries.

Although information regarding seat belt use was missing for almost 30% (892/3014) of the cohort, among those for whom this information was available, 87.6% (1859/2122) were wearing seat belts at the time of the collision. Of those wearing seat belts, most were using a three-point lap-shoulder belt (98% or 1822/1859), rather than a lap belt only. Based on the results shown in Table 2, there seemed to be a greater tendency for multiple injuries at higher speed limits. More than half of the whiplash injuries (53.8% or 1622/3014) occurred on roads where the speed limit was less than 60 km/h.

Duration of Absence

For the analysis of absence duration, the study cohort has 2810 members, since it excludes from the 3014 members the 204 subjects with a recurrence. Among these study cohort members, more than one-fifth (22.1%) recovered within one week of the collision (Table 3). Fifty-three percent took more than four weeks to recover from their injuries. One year after the event, 2.9% were still absent. Among those who sustained only a whiplash injury, 1.9% had an absence of longer than one year. The longest absence among those study cohort members who did not experience a recurrence was 1920 days. This corresponded to an exit date from the cohort of July 2, 1992.

The estimated Kaplan-Meier return to activity curve for the 2810 whiplash subjects in the study cohort who did not experience a recurrence of symptoms is shown in Figure 2.3 (truncated at 365 days). Twenty-three out of 2810 observations (0.8%) were censored because the files on these whiplash subjects were not yet closed at the time when the data were extracted from the SAAQ's computerized databases. The return to activity curve, which is a graphical representation of the data contained in Table 3, reveals that approximately 50% of the 2810 whiplash subjects recovered within one month of the collision, while 64% recovered within sixty days. At six months and one year after the collision date, the proportion of subjects who had recovered was 87% and 97%, respectively. Return to activity curves stratified by gender and age are shown in Figures 2.4 and 2.5 respectively.

Duration of Absence and Recurrence

Analyses of the mean duration of absence and rate of recurrence are shown in Table 4 for sociodemographic factors and in Table 5 for the collision-related factors. Thus, female gender, older age, increased number of dependents, married status, multiple injuries, greater collision severity, vehicle other than car or taxi, collisions other than rear-end and non-use of seat belt are associated with a longer absence. Recurrences, defined as the recurrence of symptoms of collision-related injuries, were found to have occurred in 204, or 6.8% of the study subjects. When those cohort members who sustained injuries in addition to whiplash were excluded from the analyses, the rate of recurrence was higher with rear-end collisions and the presence of dependents at home.

Since information on seat belt use was missing for nearly 30% of the subjects, these individuals were included in the group to which they were most similar with respect to time to return to activity. That is, they were reassigned to the group that was using a seat belt at the time of the collision, thus resulting in a 91% seat belt use rate.

Costs Related to Whiplash

An itemized breakdown of the collision-related expenses compensated by the SAAQ to the 4757 whiplash claimants is shown in Table 6, with all amounts provided in Canadian dollars (CAD$). This cohort cost the SAAQ a total of over CAD$18 million in reimbursements and compensation, or an average of over CAD$3800 per whiplash subject. Approximately three-quarters of this amount (CAD$13 million) was paid to subjects for the replacement of their regular income while they were unable to work or carry out their usual activities. The total amount of payments made to people with whiplash as their only injury (2802 of the 4757) was more than CAD$9 million, with replacement of regular income payments accounting for CAD$6.7 million of that amount. The average cost per subject with whiplash alone was therefore over CAD$3200.

The mean amount of reimbursement for prescriptions filled at a pharmacy by whiplash subjects in the cohort was CAD$24.20. Only 19 of the 4757 whiplash claimants, or 0.4%, were assigned to a rehabilitation program by the SAAQ. These 19 individuals received an average of CAD$74,958 in compensation and reimbursements from the SAAQ, amounting to a total of over CAD$1.4 million. This amount represented 7.8% of the total amount of money paid out by the SAAQ to members of the cohort.

Costs and Duration of Absence

Among the 4757 subjects who sustained a whiplash injury in Quebec in 1987, the 303 individuals who experienced at least one recurrence related to the injuries they sustained in the motor vehicle collision cost the SAAQ a total of CAD$2 876 964.37. This amount includes the costs incurred both before and after the recurrence since it was not possible to distinguish between these time periods from the computerized data obtained from the SAAQ. Therefore these individuals, who represented 6.4% of the full study cohort, accounted for 15.7% of the total costs paid out by the SAAQ to members of the study cohort.

Among the cohort of 2801 patients who sustained only a whiplash injury, the 61.5% whose absence lasted two months or less accounted for only 15.5% of the total costs paid out by the SAAQ for all patients in this cohort. The 26% whose absence lasted between two and six months accounted for 38.5% of the costs, while the 10.6% whose absence lasted between six and 12 months accounted for 32.3% of the costs, and the remaining 1.9% of patients still compensated 12 months after the collision accounted for 13.7% of the total costs paid by the SAAQ.

For the cohort of 1956 patients who sustained a whiplash injury along with other injuries, the corresponding proportions are similar except that the 10.5% whose absence lasted between six and 12 months accounted for only 24.3% of the costs, while 4.8% were still compensated 12 months after the collision and they accounted for 36.1% of the total costs paid by the SAAQ.