1. Ignition Interlocks As Alternatives to Hard Revocation for DWI Offenders
Richard Roth, Paul Marques, Robert Voas
Pacific Institute For Research and Evaluation
Funded by NHTSA and RWJ
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Outline
The recidivism of DWI offenders subject to 10 year hard revocation in NM, with and without interlocks
The recidivism of DWI offenders arrested between 2003 and 2005, with and without interlocks
The effect of the New Mexico Interlock License Act on interlock installation rates
Conclusions
This is what I plan to talk about in this presentation:
First, a study of the reduction in recidivism of interlocked offenders subject to 10 year license revocation in New Mexico
Then, a study of the reduction in recidivism for all DWI offenders for whom the option of legal driving with an interlock license was available in NM.
Third the effect of the New Mexico Ignition Interlock License Act on interlock installation rates.
And finally some conclusions.
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3. Persons with 3 DWI Convictions within 10 years
Group Control Interlock
Group Size ,571
14,271
1300
Prior Arrests (average)
3.78
4.28
Prior Convictions (average)
3.33
3.75
Age (average)
36.1 years
35.8 years
BAC < 0.16%
18.0%
22.1%
BAC >= 0.16%
48.4%
41.7%
Refused BAC Test
33.6%
36.2%
Gender: Male, Female, Missing
89.1%,10.9%
88.5%,10.8% 0.6%
In New Mexico, persons having 3 DWI convictions within a 10 year period are subject to a 10 year revocation of their driver’s license from the data of their last conviction. This slide is for researchers to compare the characteristics of the interlock group and the control group for this study of those subject to 10 year revocation in NM. Note that 1300 offenders subject to the 10 year revocation did install interlocks before the end of that sanction period. The characteristics were close enough to be easily adjusted for in a Cox multivariate proportional hazards regression analysis. But first of all, I calculated the simple DWI rearrest rate per year for each group.
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4. Roth Revocation Alternative Annecy
Rates are normalized to “DWI re-arrests per year”
12.5%
A 74% reductiion!
4.4%
3.3%
This control group of multiple offenders had 12.5% of their members rearrested within 1 year of the last conviction of the 3 in the 10 year period. By comparison only 3.3% of the interlock group were rearrested per year while interlocks were installed. That’s a 74% reduction from the 12.5% rate of the comparison group. For the total time from installation of interlock to the end of the study period (June 30, 2005), 4.4% of the interlock group were rearrested per year. Note that for a fair comparison, all recidivism rates were normalized to a per year basis.
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22.5%
6.0%
For a more sophisticated analysis, I plotted one-minus-survival graphs and did univariate and multivariate Cox proportional hazards regression analyses. This one-minus-survival graph shows the fraction of the control group and the interlock group that are rearrested as a function of time. Clearly a much smaller fraction of the interlocked group were rearrested at any time (measured after installation and before removal for the interlock group and measured after the 3rd conviction in 10 years for the control group).
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6. Roth Revocation Alternative Annecy
Installed Interlocks vs Controls Cox Proportional Hazards Regression Analysis
Interlock/Control (Univariate) Odds Ratio =
Multivariate
Odds Ratio
P value
95% C.I.
Age (per year)
0.9788
0.0000
Gender F/M
0.8445
0.0073
BAC High/Low
1.1605
0.0045
BAC Refused/Low
1.2200
0.0003
Arrest #
1.1461
Conviction #
0.9650
0.2406
Interlock/Control
0.2556
This slide shows the result of the Cox regression analyses for the period during which interlocks were actually installed. The simpler univariate analysis which ignores any differences in other variables between the two groups gives an a odds ratio of (p < ). The more sophisticated multivariate analysis which adjusts for the effect of age, gender, BAC, prior arrests, and prior convictions gives an almost identical result, So both all three analyses indicate that the interlock group has only 26% of the recidivism of the control group.
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7. Roth Revocation Alternative Annecy
From Installation to End of Study Period
The previous analysis was for the period during which interlocks were actually installed. This graph shows the recidivism of the interlock group from the time interlock was installed to the end of the study period, even if the interlock was removed before the end of the study period. Researchers will note that the hazards are proportional and fairly constant. The odds ratio that comes out of the Cox analyses is the average value of the ratio of the slopes of these curves.
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During and After Interlock vs Controls Cox Proportional Hazards Analysis
Univariate Analysis: IG/CG Odds Ratio =
Multivariate
Odds Ratio
P value
95% Confid
Age (per year)
0.9787
0.0000
Gender F/M
0.8412
0.0059
BAC High/Low
1.1700
0.0027
BAC Refused/Low
1.2329
0.0001
Arrest #
1.1425
Conviction #
0.9671
0.2688
Interlock/Control
0.3955
Here’s the summary of the Cox analyses for interlock recidivism during the entire study period, including the time after interlocks were removed. First of all the univariate analysis gives an odds ratio of 0.42 (p<0.0001). Next the multivariate analysis that adjusts for the values of age, gender, BAC, prior arrests, and prior convictions gives a similar result of 0.40 (p<0.0001). The recidivism of the interlock group is only 40% as large as that of the control group.
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9. Recidivism of 10 year ALR Cox Regression
Proportional Hazards Regressions
Univariate
Multivariate
While Interlocked vs Controls
0.27
0.26
During and after interlock vs Controls
0.42
0.40
This slide summarizes the results of the 4 Cox regressions, showing a 74% reduction during interlock installation and a 60 % reduction over the entire study period.
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A study of offenders arrested or interlocked between 2003 and June, 2005.
5707 offenders installed interlocks
3036 of the 5707 removed their interlocks before end of study, June 30, 2005
38,105 persons were arrested for DWI but did not install interlocks
Next I will report on a study of all of the offenders arrested or interlocked between 2003 and June, In that period 5707 persons arrested for DWI in New Mexico installed interlocks. Before the end of the study period, 53 % of the interlocked offenders, 3036 out of 5707, had removed their interlocks. The control group consisted of 38,105 persons who were arrested during the same period but did not install interlocks. Note that this study includes voluntary and mandatory installations of interlocks.
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11. 90 Days was the minimum revocation time and the maximum jail time for first offenders
Installed after 1/1/03 and removed before July 05
days
For the 3036 who removed interlocks before the end of the study period, this slide shows the distribution of installation times. You can see big peaks at 90 days and 1 year. The revocation for first offenders who did not refuse the BAC test was 90 days and the revocation for all others was 1 year. Also some judges mandated 90 day installations for first offenders because of the 90 maximum jail term for first offenders. The average installation time was 7 months (213 days) and the median was less than 6 months.
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This slide shows the fraction re-arrested for DWI while interlocks were installed compared to the control group.
It’s obvious that the interlocked group has far less recidivism.
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13. Cox Regression Results During Installation
Proportional Hazards
Regressions
Odds Ratio
Univariate
p<.001
Multivariate
Age, BAC, Prior Arrests
p<.001
Here are the results of the corresponding Cox regressions. The recidivism of the interlocked group is only 35% of that of the control group after adjusting for age, gender, BAC, and priors arrests.
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14. Half of Interlocks were removed in less than 6 months
Recall that the median installation time of interlocks was less than 6 months and that many were removed in 90 days. This slide shows recidivism from installation to the end of the study period including time after interlock removal for most interlocked offenders. This slide shows substantially less over all recidivism for the interlocked group.
Half of Interlocks were removed in less than 6 months
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15. Cox Regression Results Including After-Removal Period
Proportional Hazards
Regressions
Odds Ratio
Univariate
p<.001
Multivariate
Age, BAC, Prior Arrests
p<.001
The Cox regressions give significant odds ratios of .61 and .56.
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3300/year
June 2003-June 2005
Between January 2003 and May 2003, the interlock installation rate was 1000 per year, but after the Ignition Interlock License Act went into effect in June 2003, the rate increased to over 3000 per year. The
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In order to get an interlock license in New Mexico, an offender has to have proof of insurance and an installed interlock. In the last two years over 5000 licenses have been granted and the rate this year so far is over 3000 per year.
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Conclusions
Interlocks reduce recidivism by 65% during installation and by 44% overall.
An Interlock License Alternative to Hard Revocation triples installation rates.
In conclusion, studies in New Mexico show that interlocked offenders have many fewer DWI arrests both while interlocks are installed and over the entire study periods.
And the Interlock License Alternative to license revocation triples the interlock installation rates.
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