Suppose the age of onset for Parkinson's disease in the general population is known to have a mean of 68 years. A medical researcher selects a random sample of 32 Parkinson's patients of African American ethnicity and records the age of onset for each patient. He decides to use a one-sample t-test to determine whether age of onset for African Americans differs in some way from the general population, obtaining the SPSS output below.
One-Sample Statistics
\begin{tabular}{l|r|r|r|r}
& \( N \) & Mean & Std. Deviation & Std. Error Mean \\
\hline age of onset & 32 & 67.16 & 2.604 & 460 \\
\hline
\end{tabular}
One-Sample Test
\begin{tabular}{|c|c|c|c|c|c|c|c|}
\hline & \multicolumn{7}{|c|}{ Test Value \( =68 \)} \\
\hline & \multirow[b]{2}{*}{\( t \)} & \multirow[b]{2}{*}{ df } & \multicolumn{2}{|c|}{ Significance } & \multirow{2}{*}{\begin{tabular}{c}
Mean \\
Difference
\end{tabular}} & \multicolumn{2}{|c|}{\begin{tabular}{l}
\( 95 \% \) Confidence Interval of the \\
Difference
\end{tabular}} \\
\hline & & & One-Sided p & Two-Sided p & & Lower & Upper \\
\hline age of onset & -1.833 & 31 & .038 & .076 & -844 & -1.78 & .10 \\
\hline
\end{tabular}
One-Sample Effect Sizes
\begin{tabular}{ll|l|l|l|l|}
& & & \multicolumn{2}{c}{\( 95 \% \) Confidence Interval } \\
& Standardizer \( ^{2} \) & Point Estimate & Lower & Upper \\
\hline \multirow{2}{*}{ age of onset } & Cohen's d & 2.604 & -.324 & -.677 & .034 \\
\cline { 2 - 6 } & Hedges' correction & 2.669 & -.316 & -.661 & .033 \\
\hline
\end{tabular}
a. The denominator used in estimating the effect sizes.
Cohen's d uses the sample standard deviation.
Hedges' correction uses the sample standard deviation, plus a correction factor.