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C. Results

1. Franklin County

Pooled results for all drivers. Table IV-3 shows that for both first and second DWS drivers pooled together, impounding and/or immobilizing the vehicle marginally reduced the number of DWS offenses but not the number of DUI offenses during the sanction period. This marginal effect may be due to the relatively short time (30 or 60 days) during which a DWS offender’s vehicle was normally impounded or immobilized. The notable feature of the upper portion of this table is that these DWS drivers experienced zero repeat offenses during the time their vehicles were not available to them. Despite this, the number of cases in the sanctioned group was so small, and the amount of exposure time available was so short, that the 100% differences between the vehicle sanctioned and no-vehicle sanctioned groups were, with two exceptions, not statistically significant.

This may be a case where more attention should be given to the effect size to avoid a "type two error." The effect sizes displayed in Tables IV-3 through IV-6 are a measure of the relative difference between the sanctioned group’s rate of reoffense and the comparison group’s rate of reoffense, using the latter group’s rate as the baseline or denominator. Thus, if the comparison group’s rate were 0.20 and the sanctioned group’s rate were 0.12 (i.e., 60% of the baseline rate), the relative difference would be -40%. Obviously, the largest reduction possible is necessarily bounded at 100%, when the sanctioned group’s rate is zero, but the largest increase is not bounded at +100% (which would represent a doubling-in rate).

In the lower section of Table IV-3, which gives the results for the DUI driver groups (where, as above, the total period of vehicle action is evaluated by combining the impoundment and immobilization periods), the relative differences are large: above 50% for both DWS and DUI offenses. DWS and DUI offenses are significantly reduced during the sanction period in both the Cox Regression and Kaplan-Meier analyses. Figure IV-1 shows the cumulative DUI offense hazard (recidivism) rates during sanction using the overall Cox Regression model fit based on the two DWS and two DUI driver groups pooled, which demonstrates a clear separation between those DWS and DUI offenders who actually received a vehicle action (solid line) and comparison drivers who were eligible but avoided the sanction (dashed line).

The upper section of Table IV-4 gives the results of the analysis of the DWS groups up to 2 years following the return of the vehicle to the offender. With the exception of DWS offenses for second DWS drivers, all of the relative differences are in the right direction, but none are significant. It appears that in the case of the DWS drivers, the sanction had no impact on DWS or DUI offenses after the vehicle was returned.

In contrast to the DWS drivers, the DUI drivers whose vehicles were impounded or immobilized for longer periods demonstrated significant reductions in DUI and DWS offenses after the vehicles were returned. The recidivism rate for DUI offenses of second DUI offenders following return of the vehicle was 22% to 38% lower than for offenders who were eligible but did not receive a vehicle sanction. These differences in rates are corrected for variations in age and prior driving record through the entry of these factors as covariates in the Cox Regression analysis (right-hand columns of Table IV-4).

Figure IV-2 shows the pooled cumulative hazard rates for the DUI offense after sanction across both DWS and both DUI driver groups, using the overall Cox Regression model fit. The solid line shows the accumulation of new offenses by the sanctioned group, while the dashed line shows the cumulative rate of DUI offenses for the comparison drivers. The origin of the graph is set at the time when the experimental group had their vehicles returned. The origin for the comparison group is set at the average time after conviction when the sanctioned group had their vehicles returned. The experimental group of drivers who received the vehicle sanction clearly had fewer DUI convictions than similar offenders not sanctioned in the months following return of their vehicles.

Table -1
Offenses during sanction period for DWS and DUI drivers in Franklin County

   
Impound group
exposure
Comparison group
exposure
Offense rate
Kaplan-Meier
Cox Regression
Driver
group
Penalty
days
Subjects
(Man-
months)
Re-
offenders
Subjects
(Man-
months)
Re-
offenders
VI/I
Non-
VI/I
Relative
diff.
Tarone-
Ware
Prob.
Relative
diff.
Wald
Prob.
Driving-while-suspended (DWS) offenders
DWS offenses
1st DWS
30
136
132
0
454
444
16
0.0%
3.5%
100%
4.68
.031*
100%
---
---
2nd DWS
60
21
40
0
70
133
5
0.0%
7.1%
100%
1.48
.223
100%
---
---
Pooled DWS groups
157
172
0
524
577
21
0.0%
4.0%
100%
5.64
.018*
100%
---
---
DUI offenses
1st DWS
30
136
132
0
454
447
3
0.0%
0.7%
100%
0.87
.352
100%
---
---
2nd DWS
60
21
40
0
70
136
2
0.0%
2.9%
100%
0.59
.443
100%
---
---
Pooled DWS groups
157
172
0
524
583
5
0.0%
1.0%
100%
1.26
.262
100%
---
---
Driving-under-the-influence (DUI) offenders
DWS offenses
2nd DUI
90
686
1953
8
970
2831
34
1.2%
3.5%
66%
8.05
.005*
39%
6.42
.011*
3rd DUI
180
134
724
4
328
1884
20
3.1%
6.1%
49%
1.42
.233
22%
0.85
.357
Pooled DUI groups
820
2677
12
1298
4715
54
1.5%
4.2%
65%
9.45
.002*
34%
6.78
.009*
DUI offenses
2nd DUI
90
686
1937
12
970
2813
36
1.8%
3.7%
52%
4.90
.027*
29%
4.14
.042*
3rd DUI
180
134
729
3
328
1877
21
2.4%
6.4%
63%
2.81
.094
37%
2.28
.131
Pooled DUI groups
820
2666
15
1298
4690
57
1.8%
4.4%
58%
6.93
.009*
30%
5.72
.017*

Table -2
Offenses after sanction period for DWS and DUI drivers in Franklin County

   
Impound group
exposure
Comparison group
exposure
Offense rate
Kaplan-Meier
Cox Regression
Driver
group
Penalty
days
Subjects
(Man-
months)
Re-
offenders
Subjects
(Man-
months)
Re-
offenders
VI/I
Non-VI/I
Relative
diff.
Tarone-
Ware
Prob.
Relative
diff.
Wald
Prob.
Driving-while-suspended (DWS) offenders
DWS offenses
1st DWS
30
134
1486
14
431
3962
50
13.2%
17.1%
23%
0.76
.382
8%
0.32
.570
2nd DWS
60
19
235
3
58
494
6
17.6%
14.7%
-20%
0.12
.733
-43%
0.88
.347
Pooled DUI groups
153
1721
17
489
4456
56
13.8%
16.7%
18%
0.67
.415
3%
0.07
.793
DUI offenses
1st DWS
30
135
1568
6
444
4363
21
5.1%
6.4%
21%
0.11
.735
19%
0.77
.380
2nd DWS
60
19
274
0
61
572
3
0.0%
3.1%
100%
1.91
.167
100%
---
---
Pooled DUI groups
154
1842
6
505
4935
24
4.4%
5.6%
26%
0.22
.639
24%
1.42
.234
Driving-under-the-influence (DUI) offenders
DWS offenses
2nd DUI
90
671
7800
48
873
8827
75
6.8%
11.0%
38%
3.33
.068
11%
1.49
.222
3rd DUI
180
125
1333
5
242
2005
20
4.3%
11.8%
63%
4.27
.039*
33%
2.53
.112
Pooled DUI groups
796
9133
53
1115
10832
95
6.4%
11.1%
42%
4.86
.028*
13%
2.67
.102
DUI offenses
2nd DUI
90
669
7922
33
871
8877
63
5.0%
8.0%
38%
6.27
.012*
22%
5.03
.025*
3rd DUI
180
126
1309
9
243
2030
15
7.3%
9.4%
23%
0.02
.901
-3%
0.02
.899
Pooled DUI groups
795
9231
42
1114
10907
78
5.3%
8.2%
35%
6.08
.014*
18%
4.13
.042*

Figure -1
Proportion of drivers committing a DUI offense during sanction period in Franklin County
(Pooled Model Fit, Cox Regression Analysis)

Figure -2
Proportion of drivers committing a DUI offense after sanction period in Franklin County
(Pooled Model Fit, Cox Regression Analysis)

Hamilton County

Pooled results for all drivers. In the Hamilton County recidivism analysis, there was no need to consider combining vehicle immobilization and vehicle impoundment since, with few exceptions, vehicles were simply impounded for the length of the sanction period. The two upper sets of rows of Table IV-5 present the Cox Regression and Kaplan-Meier analyses of recidivism rates for DWS drivers during the sanction period. These analyses found significant reductions in DWS offenses, but not DUI offenses, for the combined groups of drivers. The effect sizes for DWS offenses was large, running between 45% and 75%. The reductions in DWS and DUI offense rates for the experimental group of DUI drivers are generally larger than those demonstrated by the DWS drivers whose vehicles were impounded for a shorter time. Pooled effect sizes for both DWS and DUI offenses varied from 40 to 60%. Figure IV-3 shows the pooled cumulative hazard rates for DUI offenses across the two DWS and two DUI driver groups during the sanction period using the overall Cox Regression model fit.

Table IV-6 provides the results of the analysis for DWS and DUI offenses in the postsanction period. The Kaplan-Meier analysis shows some differences in the DWS recidivism for the DWS drivers; however, this was not confirmed in the Cox Regression analysis. In any case, the effects sizes were too small to be of interest. Both the Cox Regression and the Kaplan-Meier analytical procedures detected significant reductions during the postsanction period in both DWS and DUI offenses for the DUI drivers. The Cox regression yielded an effect size of 30% for DUI offenses. Figure IV-4 shows the pooled cumulative hazard rates for DUI offenses across the two DWS and two DUI driver groups after the vehicles were returned to the offenders, using the overall Cox Regression model fit.

Table -3
Offenses during sanction period for DWS and DUI drivers in Hamilton County

   
Impound group
exposure
Comparison group
exposure
Offense rate
Kaplan-Meier
Cox Regression
Driver
group
Penalty days
Subjects
(Man-months)
Re-offenders
Subjects
(Man-months)
Re-offenders
VI/I
Non-
VI/I
Relative
diff.
Tarone-Ware
Prob.
Relative diff.
Wald
Prob.
Driving-while-suspended (DWS) offenders
DWS offenses
1st DWS
30
676
497
3
454
444
10
0.6%
2.2%
71%
4.22
.040*
47%
3.65
.056
2nd DWS
60
205
326
3
70
133
5
1.8%
7.1%
74%
4.39
.036*
50%
3.67
.055
Pooled DUI groups
881
823
6
524
577
15
1.0%
3.8%
74%
6.97
.008*
45%
5.89
.015*
DUI offenses
1st DWS
30
676
497
3
454
447
2
0.6%
0.4%
-42%
0.14
.713
-19%
0.14
.707
2nd DWS
60
205
328
0
70
136
2
0.0%
2.9%
100%
4.91
.027*
100%
---
---
Pooled DUI groups
881
825
3
524
583
4
0.4%
1.2%
67%
0.07
.792
26%
0.63
.427
Driving-under-the-influence (DUI) offenders
DWS offenses
2nd DUI
90
533
1340
2
970
2831
29
0.5%
3.0%
84%
9.18
.002*
61%
6.80
.009*
3rd DUI
180
347
1582
8
328
1884
18
3.1%
5.5%
44%
2.39
.122
45%
4.22
.040*
Pooled DUI groups
880
2922
10
1298
4715
47
1.7%
4.1%
60%
11.47
.001*
41%
8.94
.003*
DUI offenses
2nd DUI
90
533
1335
3
970
2813
31
0.7%
3.2%
80%
8.92
.003*
56%
7.18
.007*
3rd DUI
180
347
1587
7
328
1877
16
2.7%
4.9%
44%
2.59
.108
28%
2.06
.152
Pooled DUI groups
880
2922
10
1298
4690
47
1.6%
4.0%
60%
11.51
.001*
41%
9.34
.002*

 

Table -4
Offenders after sanction period for DWS and DUI drivers in Hamilton County

   
Impound group
exposure
Comparison group
exposure
Offense rate
Kaplan-Meier
Cox Regression
Driver
group
Penalty days
Subjects
(Man-months)
Re-offenders
Subjects
(Man-months)
Re-offenders
VI/I
Non-VI/I
Relative diff.
Tarone-Ware
Prob.
relative diff.
Wald
Prob.
Driving-while-suspended (DWS) offenders
DWS offenses
1st DWS
30
639
7707
90
431
3976
50
8.6%
15.7%
46%
4.44
.035*
1%
0.03
.869
2nd DWS
60
185
2070
28
58
476
6
12.5%
13.7%
9%
0.26
.611
3%
0.01
.905
Pooled DUI groups
824
9777
118
489
4452
56
9.3%
15.3%
39%
4.69
.030*
3%
0.14
.713
DUI offenses
1st DWS
30
637
7892
29
445
4378
22
4.4%
6.4%
32%
1.67
.197
8%
0.35
.557
2nd DWS
60
190
2229
5
61
554
3
2.2%
3.0%
28%
1.64
.200
46%
2.55
.110
Pooled DUI groups
827
10121
34
506
4932
25
4.0%
5.8%
31%
2.07
.150
10%
0.66
.417
Driving-under-the-influence (DUI) offenders
DWS offenses
2nd DUI
90
490
5395
47
888
9146
79
7.2%
10.8%
33%
1.92
.166
4%
0.23
.635
3rd DUI
180
288
2875
22
260
2178
22
5.6%
11.8%
53%
4.17
.041*
20%
3.32
.068
Pooled DUI groups
778
8270
69
1148
11324
101
6.8%
11.1%
39%
3.95
.047*
9%
1.28
.257
DUI offenses
2nd DUI
90
489
5418
19
885
9195
66
3.6%
8.0%
56%
9.15
.003*
30%
7.51
.006*
3rd DUI
180
290
2886
9
264
2206
20
4.0%
9.5%
58%
7.97
.005*
33%
3.63
.057
Pooled DUI groups
779
8304
28
1149
11401
86
3.7%
8.4%
56%
14.71
.001*
31%
11.35
.001*

Figure -3
Proportion committing DUI during immobilization sanction in Hamilton County
(Pooled Model Fit, Cox Regression Analysis)

Figure -4
Proportion committing DUI after immobilization sanction in Hamilton County
(Pooled Model Fit, Cox Regression Analysis)

D. Discussion

Limitations in these studies. The principle limitation in these results is that the sanctions could not be assigned to offenders at random. The imposition of the vehicle penalty occurred or did not occur as a result of several factors. Some factors such as administrative problems or lack of resources for the police and courts may have had a minimal impact on subject characteristics and, therefore, probably did not bias the group comparisons. Other factors–offender’s choice (retaining a lawyer, pleading guilty, etc.) and differences between judges’ sentencing practices–may have produced significant differences between the experimental group of offenders whose vehicles were held under the VA law and the comparison group whose vehicles were not held.

Table IV-7 shows the differences in age and history of driving offenses between the drivers whose vehicles were impounded and not impounded in both Franklin and Hamilton Counties. These two measures–age and prior driving offenses–were available for use as covariates for reducing any bias produced by the many factors that entered the selection of those actually impounded or immobilized. (Gender information was also available, but there were too few females to make this factor a useful covariate.) The upper portion of Table V-7 shows that Franklin County’s sanctioned driver group had mean values for the two age categories and the two types of prior-offense categories that were generally similar to those for the comparison driver group. The one exception was the second DWS offenders (60-day group) where the sanctioned group was almost twice as likely to have had one prior DWS offense.

The age and prior record variables for Hamilton County appear in the lower portion of Table IV-7. As can be seen, there is somewhat more variability between the sanctioned driver group and the comparison driver group in this county. The comparison group of DWS drivers appears to have had more prior DWS and DUI offenses than the sanctioned group. The potential effect of these differences between groups in Hamilton County were reduced by the use of these variables in the Cox Regression analysis, which generally provided the same results as the Kaplan-Meier analysis.

Driver’s license status (shown in Section II as an important factor in determining DUI offense rates) was not a factor in the observed differences in recidivism during the vehicle sanction because all DWS and DUI offenders were suspended during the vehicle action period. In the later part of the after-impoundment period, some second DUI drivers may have been reinstated. However, the relatively few reinstated cases and the relatively small number of drivers followed beyond one year suggest that driver’s license status had little effect on the results reported in this Section.

Table -5
Means for comparison and sanctioned groups of drivers in Franklin and Hamilton Counties

 
30
60
90
180
covariates
cmpsn
sanc-tioned
cmpsn
sanc-tioned
cmpsn
sanc-tioned
cmpsn
sanc-tioned
FRANKLIN COUNTY
Age
30.8
29.8
30.1
31.9
33.6
33.2
35.4
34.0
Age >25
0.348
0.383
0.286
0.286
0.168
0.212
0.090
0.128
Age 40+
0.141
0.119
0.190
0.214
0.199
0.193
0.256
0.201
*prior DUIs
0.513
0.404
0.688
0.694
0.834
0.872
1.240
1.271
*prior DWS
0.479
0.451
0.673
1.115
0.210
0.268
0.272
0.388
HAMILTON COUNTY
Age
29.5
31.8
32.4
30.0
33.0
34.4
34.0
35.5
Age >25
.383
.278
.286
.360
.212
.184
.128
.112
Age 40+
.119
.168
.214
.140
.194
.247
.201
.256
*prior DUIs
.404
.245
.694
.103
.872
.635
1.271
.807
*prior DWS
.451
.287
1.115
.780
.268
.262
.388
.350
*Within the most recent 3-year period only. Number of priors were log-transformed due to highly skewed distributions.

 

 

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