## 6 Results (Study 2)
### Phase 1: Performance Differences Between Age Groups on FOD--Advanced Combination 3
The effect size approximates the magnitude of the relationship between two variables. A Cohen's \(d\) measure of effect size was determined for the four significant variables at \(\alpha<0.01\) and for the three variables significant at \(\alpha<0.05\), where a higher value represents a stronger effect of the dependent variable (simulator performance variable) on the independent variable (age group). With regard to effect size, the variables that were significant at the alpha level of 0.01 also had greater effect sizes. In order from greatest to least, the number of target E extra presses (\(d=1.18\)), standard deviation of brake reaction time (\(d=1.11\)), average target E reaction time (\(d=1.06\)), and standard deviation of target E reaction time (\(d=0.87\)) had a large effect (e.g., \(d>0.8\)). All variables reported significant at the alpha level of 0.05 had a moderate effect. The effect size results, from greatest to least, were average brake reaction \begin{table}
\begin{tabular}{c c c c c c} \hline  & \multicolumn{2}{c}{**Means**} & \multicolumn{2}{c}{**\(t\)-Statistic**} & \multicolumn{2}{c}{**\(p\)-Value**} & \multicolumn{2}{c}{**Effect Size (\(d\))**} \\ \multicolumn{2}{c}{**Performance Variables**} & \multicolumn{2}{c}{**Teens (N = 21)**} & \multicolumn{2}{c}{**Seniors (N = 34)**} & & \\ \hline Percent of target Es detected & 97.8 & 93.9 & \(-2.551\) & 0.014 & 0.65 \\ \hline Average target E reaction time (s) & 1.4 & 1.7 & 4.081 & \textless{}0.001 * & 1.06 \\ \hline SD of target E reaction time (s) & 0.4 & 0.5 & 3.325 & \textless{}0.002 * & 0.87 \\ \hline Number of target E extra presses & 0.2 & 1.01 1 & 4.512 & \textless{}0.001 * & 1.18 \\ \hline Number of distractor E presses & 0.6 & 1.3 & 1.946 & 0.057 & 0.51 \\ \hline Percent of brake lights detected & 96.8 & 92 & \(-2.622\) & 0.012 & 0.67 \\ \hline Average brake reaction time (s) & 1.2 & 1.4 & 2.595 & 0.012 & 0.72 \\ \hline SD of brake reaction time (s) & 0.3 & 0.4 & 4.008 & \textless{}0.001 * & 1.11 \\ \hline Number of brake extra presses & 0.9 & 1.6 & 1.408 & 0.165 & 0.39 \\ \hline Percent of time in lane & 99.8 & 99.8 & 0.011 & 0.991 & 0.00 \\ \hline Number of lane excursions & 0.1 & 0.1 & \(-0.063\) & 0.950 & 0.02 \\ \hline Average speed (mph) & 28.8 & 27.7 & \(-0.593\) & 0.556 & 0.16 \\ \hline Variability of speed (mph) & 3.7 & 4.4 & 1.338 & 0.187 & 0.37 \\ \hline \end{tabular} Note: Significance codes: *\({}^{\prime\prime}\) a = 0.0038 which is the Bonferroni-corrected Type I error rate for 13 comparisons.  
\end{table} 
Table 5: Independent-samples \(t\)-test results for teens and seniors on driving simulator performance variables in FOD—Advanced combination 3.  
time (\(d\) = 0.72), percent of brake lights detected (\(d\) = 0.67), and percent of target Es detected (\(d\) = 0.65). The results of the independent-samples \(t\)-tests revealed four significant driving simulator variables that will be used as the dependent variables to distinguish between teen and senior participants in the LDA: average target E reaction time, standard deviation of target E reaction time, number of target E extra presses, and standard deviation of brake reaction time. Phase 2: Classification of Teens and Seniors Using the Significant Variables in Fond--Advanced Combination 3  
The LDA was conducted using four significant driving simulator variables as the dependent variables and age group as the independent variable. As previously mentioned, an LDA is a classification analysis that results in a discriminant function. In Study 1, the independent variable (FOD-A combinations) had four levels, so there were three possible discriminant functions (\(4-1\)). Because the independent variable (age group) in Study 2 has two levels, there can only be one discriminant function. A discriminant function is an equation containing estimated weights that indicate the relative influence for each dependent variable. To quantify the contribution of a specific dependent variable, the weight must first be converted to an absolute value.