For the Following Data, What Is the Mean of the Difference

Multiple Choice

For the following data, what is the mean of the difference scores? $$\begin{array} { | r r } \hline { \text { Before } } & \text { After } \\\hline 160 & 153 \\\hline 125 & 124 \\\hline 142 & 136 \\\hline 187 & 167 \\\hline\end{array}$$

A) 8.50
B) 5.00
C) 4.26
D) 11.33