A safety analyst wants to compare the variability in steering correction times for experienced and inexperienced drivers on three types of roads: paved, gravel, and dirt. The analyst records the time in seconds that each driver uses to make steering corrections on each type of road.
- Open the sample data, RoadConditions.MTW.
- Choose .
- Select Response data are in one column for all factor levels.
- In Response, enter 'Correction Time'.
- In Factors, enter Experience and RoadType.
- Click OK.
Interpret the results
In this summary plot, the p-values of 0.943 and 0.830 are greater than the common significance level of 0.05. None of the differences between the groups are statistically significant, and all the comparison intervals overlap.
Test for Equal Variances: Correction Time versus Experience, RoadType
Method
Null hypothesis All variances are equal
Alternative hypothesis At least one variance is different
Significance level α = 0.05
95% Bonferroni Confidence Intervals for Standard Deviations
Experience RoadType N StDev CI
Advanced Dirt 4 5.09902 (0.45310, 168.555)
Advanced Gravel 4 4.16333 (0.42041, 121.108)
Advanced Paved 4 3.87298 (0.31299, 140.776)
Beginner Dirt 4 6.05530 (1.01104, 106.529)
Beginner Gravel 4 4.76095 (0.89964, 74.009)
Beginner Paved 4 5.88784 (0.52320, 194.630)
Individual confidence level = 99.1667%
Tests
Test
Method Statistic P-Value
Multiple comparisons — 0.943
Levene 0.42 0.830