Appendix C
Supplementary Statistical Results
Tables C1 through C7 present the outcomes of the LOGISTIC procedure using the Statistical Analysis System (SAS).^{1} Listed are:

The name of each parameter included in the model;

The degrees of freedom (DF) associated with each parameter;

The estimated coefficient of the parameter, obtained by maximumlikelihood estimation;

The standard error of the coefficient (a measure of precision);

The Wald Chisquare statistic, computed as the square of the value obtained by dividing the parameter estimate by its standard error; and

The pvalue (Pr > ChiSq) for the Wald Chisquare statistic with 1 DF, with a value below 0.05 indicating a significant effect of the associated model parameter if a 5 percent significance level is chosen.
The parameters included in the logistic model are the static stability factor (SSF) and the five “dummy” state variables (i.e., 0,1 variables). Note that Missouri, the sixth state in the data, is omitted in the model; it is the baseline state in the model. For example, using the modeling results shown in Table C1 and the notation of Equation 7 in Chapter 3, the logit model can be written as follows:
where P is the estimated probability of a rollover given a singlevehicle crash, and the adjustments are as follows:
−0.1910 
if STORM = 1 (+0 otherwise) 
+0.9276 
if FAST = 1 (+0 otherwise) 
+0.1279 
if HILL = 1 (+0 otherwise) 
+0.5224 
if CURVE = 1 (+0 otherwise) 
−0.0913 
if MALE = 1 (+0 otherwise) 
+0.3187 
if YOUNG = 1 (+0 otherwise) 
−0.3664 
if OLD = 1 (+0 otherwise) 
+0.2578 
if DRINK = 1 (+0 otherwise) 
+1.1611 
if State = Florida (+0 otherwise) 
+0.7852 
if State = Maryland (+0 otherwise) 
+0.8006 
if State = North Carolina (+0 otherwise) 
+1.2121 
if State = Pennsylvania (+0 otherwise) 
+1.4575 
if State = Utah (+0 otherwise) 
TABLE C1 Logit Model Results for Data from Six States Combined (See Figure 32)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
1.5326 
0.0555 
762.6947 
<.0001 
SSF 
1 
3.6027 
0.0416 
7510.7110 
<.0001 
STORM 
1 
0.1910 
0.0130 
214.9444 
<.0001 
FAST 
1 
0.9276 
0.0123 
5642.4241 
<.0001 
HILL 
1 
0.1279 
0.0124 
106.9493 
<.0001 
CURVE 
1 
0.5224 
0.0122 
1844.5867 
<.0001 
MALE 
1 
0.0913 
0.0123 
55.2705 
<.0001 
YOUNG 
1 
0.3187 
0.0119 
720.3518 
<.0001 
OLD 
1 
0.3664 
0.0405 
81.6902 
<.0001 
DRINK 
1 
0.2578 
0.0157 
270.7577 
<.0001 
dummy_fl 
1 
1.1611 
0.0214 
2953.9104 
<.0001 
dummy_md 
1 
0.7852 
0.0257 
932.6290 
<.0001 
dummy_nc 
1 
0.8006 
0.0192 
1742.2279 
<.0001 
dummy_pa 
1 
1.2121 
0.0200 
3686.3054 
<.0001 
dummy_ut 
1 
1.4575 
0.0296 
2417.7396 
<.0001 
TABLE C2 Logit Model Results for Data from Six States Combined for Risk Scenario Close to the Minimum (See Figure 33)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
1.0804 
2.8127 
0.1476 
0.7009 
SSF 
1 
3.7387 
2.0212 
3.4216 
0.0643 
dummy_fl 
1 
0.7377 
0.7845 
0.8842 
0.3470 
dummy_md 
1 
0.5256 
1.0138 
0.2688 
0.6042 
dummy_nc 
1 
0.5774 
0.8119 
0.5058 
0.4770 
dummy_pa 
1 
0.4725 
0.8263 
0.3270 
0.5675 
dummy_ut 
1 
1.9178 
1.2993 
2.1786 
0.1399 
TABLE C3 Logit Model Results for Data from Six States Combined for Risk Scenario at the 25th Percentile (See Figure 34)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
1.9149 
0.3158 
36.7562 
<.0001 
SSF 
1 
3.7359 
0.2384 
245.5733 
<.0001 
dummy_fl 
1 
1.1069 
0.1341 
68.1204 
<.0001 
dummy_md 
1 
0.7083 
0.1964 
13.0090 
0.0003 
dummy_nc 
1 
0.7284 
0.1494 
23.7583 
<.0001 
dummy_pa 
1 
1.1200 
0.1415 
62.6115 
<.0001 
dummy_ut 
1 
1.0745 
0.2143 
25.1399 
<.0001 
TABLE C4 Logit Model Results for Data from Six States Combined for Risk Scenario at the Mean (See Figure 35)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
3.1380 
0.3896 
64.8641 
<.0001 
SSF 
1 
4.1671 
0.3083 
182.6660 
<.0001 
dummy_fl 
1 
1.0949 
0.1610 
46.2240 
<.0001 
dummy_md 
1 
0.7980 
0.1861 
18.3786 
<.0001 
dummy_nc 
1 
0.4573 
0.1555 
8.6466 
0.0033 
dummy_pa 
1 
1.0435 
0.1521 
47.0791 
<.0001 
dummy_ut 
1 
1.3395 
0.1965 
46.4858 
<.0001 
TABLE C5 Logit Model Results for Data from Six States Combined for Risk Scenario at the Median (See Figure 36)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
2.8052 
0.2493 
126.5779 
<.0001 
SSF 
1 
3.9525 
0.1990 
394.5406 
<.0001 
dummy_fl 
1 
1.4559 
0.0895 
264.3365 
<.0001 
dummy_md 
1 
0.6796 
0.1198 
32.1621 
<.0001 
dummy_nc 
1 
0.4733 
0.0885 
28.6180 
<.0001 
dummy_pa 
1 
0.9663 
0.0978 
97.6930 
<.0001 
dummy_ut 
1 
1.8160 
0.1236 
215.9163 
<.0001 
TABLE C6 Logit Model Results for Data from Six States Combined for Risk Scenario at the 75th Percentile (See Figure 37)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
4.1884 
0.4747 
77.8564 
<.0001 
SSF 
1 
4.9957 
0.3954 
159.5922 
<.0001 
dummy_fl 
1 
0.7393 
0.1901 
15.1233 
0.0001 
dummy_md 
1 
0.8961 
0.2166 
17.1126 
<.0001 
dummy_nc 
1 
0.3376 
0.1571 
4.6142 
0.0317 
dummy_pa 
1 
1.2998 
0.1448 
80.5297 
<.0001 
dummy_ut 
1 
1.6824 
0.2122 
62.8738 
<.0001 
TABLE C7 Logit Model Results for Data from Six States Combined for Risk Scenario Close to Maximum (See Figure 38)
Parameter 
DF 
Estimate 
Standard Error 
Wald ChiSquare 
Pr > ChiSq 
Intercept 
1 
0.7049 
0.5683 
1.5388 
0.2148 
SSF 
1 
1.7458 
0.4509 
14.9929 
0.0001 
dummy_fl 
1 
1.5017 
0.1989 
56.9796 
<.0001 
dummy_md 
1 
0.3726 
0.5993 
0.3865 
0.5342 
dummy_nc 
1 
1.6822 
0.1713 
96.4075 
<.0001 
dummy_pa 
1 
0.7427 
0.2205 
11.3456 
0.0008 
dummy_ut 
1 
2.2298 
0.4830 
21.3100 
<.0001 