Paired T-Test

greater extent.

of Parkinson's Disease upon Decision Making Ability and Driving Performance 327

change in Driving Performance Score between trials for both groups, whilst Figure 8 shows

**(n=8) Mean (SD)** 

82.7 (6.0) 59.2 (17.9) -23.5 (19.1)

864.8 (172) 776 (110) -88.6 (73.0)

Table 7. Driving Performance and Scenario Completion Time for Trial One and Two

The Driving Performance Scores of both groups decreased in Trial 2. However, the extent of this decline was significantly greater for the drivers with PD (t-test p=0.01). These results were confirmed by Wilcoxon test (p=0.03) (refer to Table 7). Although the driving performance of the driver with PD was lower under time pressure, the driving performance

The control group had a greater variance in Driving Performance Scores compared with the drivers with PD in both trials, as shown by Figure 7. When under a time pressure, the

Figure 8 shows the difference within each group for the Scenario Completion Time for trial one and trial two. All participants in both groups, except one control participant, completed the second trial faster as required. In trial one, there were four outliers in the control group as shown by the dots in Figure 8. Both groups were able to significantly decrease their Scenario Completion Time; however the control group was able to decrease their score to a

**3.3.1 Comparison between the driving performance of the groups** 

variance in Driving Performance Scores of the drivers with PD increased.

**3.3.2 Group comparison of scenario completion time** 

**Control Group (n=13) Mean (SD)** 

> 76.5 (22.4) 67.4 (27.3) - 9.2 (24.4)

782 (137) 674 (64) -107.5 (103.8) **Results** 

**p-value** 

0.36 0.47 0.17

0.01\*# 0.02\*^ 0.20# 0.16^

> 0.21 0.02\* 0.66

0.01\*# 0.01^ 0.01\*# 0.01^


movements between the two groups. There were no statistical differences between groups on the E-Prime Test, Symbol Digit Modalities Test, Digit Vigilance Test and Trail Making Test B.

\*Results were statistically significant (p<0.05)

\*\* 8 drivers with PD and 13 control group participants were assessed using the E-Prime Assessment.

Table 6. Participant Psychometric Assessment Results

## **3.3 Driving simulator results**

Two participants, one control and one driver with PD requested additional practice in using the simulator. All other participants began the assessment trials immediately following the practice session. During the assessment process, three drivers with PD and four control participants experienced simulator-induced motion sickness and withdrew. Their partial data was included in the data analyse where appropriate. An Independent t-test was used to determine if there was a difference between each group on the Driving Performance Score and the Scenario Completion Time for each trial. The results are shown in Table 7. The parametric t-test was found to be appropriate for analysing these results as the pre-post nature of assessment doubled the data entries available for analysis; fulfilling the sample size requirements (Hedges, 2009). Of note is that the difference between scenario completion times for Trial 2 had a p-value of 0.014 (refer to Table 7).

This however does not represent a difference between groups as the baseline performance in Trial 1 was dissimilar for each group and this disparity affects the results of Trial 2. The results shown in Table 7 are displayed in two box-and-whisker plots. Figure 7 represents the


change in Driving Performance Score between trials for both groups, whilst Figure 8 shows the change in Scenario Completion Time for each trial.

\* Results are statistically significant (p < 0.05)

^ Wilcoxon Two-sample Signed Rank Test
