A psychologist wishes to determine whether drinking coffee improves one's mood. The psychologist hangs out at the Café Coffay and asks customers to fill out a 10-point good-mood, bad-mood questionnaire (where 10 = great mood and 1 = bad mood) before and after their first cup of coffee that day. The research question is whether there is any evidence that drinking coffee improves mood.$\begin{array}{lll}&\text { Before Mood Rating }&\text { After Mood Rating }\
\hline \text { Participant 1 } & 5 & 9 \
\text { Participant 2 } & 3 & 8 \
\text { Participant 3 } & 9 & 9 \
\text { Participant 4 } & 3 & 8 \
\text { Participant 5 } & 2 & 7 \
\text { Participant 6 } & 4 & 9 \
\text { Participant 7 } & 1 & 10\
\text { Participant 8 } & 8 & 8 \
\text { Participant 9 } & 6 & 5 \
\text { Participant 10 } & 7 & 7 \
\text { Participant 11 } & 4 & 3 \
\text { Participant 12 } & 3 & 10 \
\text { Participant 13 } & 8 & 7 \
\text { Participant 14 } & 7 & 9 \
\text { Participant 15 } & 5 & 9\\hline
\end{array}$
-The df for this problem are
A)0
B)8
C)5
D)14

Question

Quizplus · Accepted Answer

The degrees of freedom (df) for a paired samples t-test (which is appropriate for this before-and-after design) is calculated as $n - 1$, where $n$ is the number of pairs. Here, $n = 15$ (the number of participants), so $df = 15 - 1 = 14$.

A Psychologist Wishes to Determine Whether Drinking Coffee Improves One's