Questions: Positive events are great, but recent research suggests that unexpected positive outcomes (e.g., an unseasonably sunny day) predict greater-than-normal amounts of risk-taking and gambling (Otto, Fleming, Glimcher, 2016). Researchers demonstrated this by comparing lottery sales-indicative of risk-taking-on normal days with lottery sales on days when some unexpected positive event occurred in the city. They observed increased sales after unexpected positive outcomes. Suppose that a researcher extends this observation to the laboratory and randomly assigns participants to two groups. Group 1 receives an unexpectedly large payment for participating and Group 2 receives the expected amount of compensation. The researcher then measures how much money the participants are willing to gamble in a game of chance.
Unexpected Positive Outcome Expected Outcome
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n=16 n=16
M=5.75 M=5.00
SS=6.5 SS=10.0
Test the one-tailed hypothesis that an unexpected positive outcome increased the amount of money that participants were willing to gamble. Use a α=.01.
Transcript text: Positive events are great, but recent research suggests that unexpected positive outcomes (e.g., an unseasonably sunny day) predict greater-than-normal amounts of risk-taking and gambling (Otto, Fleming, & Glimcher, 2016). Researchers demonstrated this by comparing lottery sales-indicative of risk-taking-on normal days with lottery sales on days when some unexpected positive event occurred in the city. They observed increased sales after unexpected positive outcomes. Suppose that a researcher extends this observation to the laboratory and randomly assigns participants to two groups. Group 1 receives an unexpectedly large payment for participating and Group 2 receives the expected amount of compensation. The researcher then measures how much money the participants are willing to gamble in a game of chance.
\begin{tabular}{cc}
\hline \begin{tabular}{c}
Unexpected \\
Positive \\
Outcome
\end{tabular} & \begin{tabular}{c}
Expected \\
Outcome
\end{tabular} \\
\hline$n=16$ & $n=16$ \\
$M=5.75$ & $M=5.00$ \\
$S S=6.5$ & $S S=10.0$ \\
\hline
\end{tabular}
Test the one-tailed hypothesis that an unexpected positive outcome increased the amount of money that participants were willing to gamble. Use a $\alpha=.01$.
Solution
Solution Steps
Step 1: Standard Error Calculation
The standard error \( SE \) is calculated using the formula:
\[
SE = \sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}
\]
Given that both sample variances \( s_1^2 \) and \( s_2^2 \) are \( 0 \) (since all values in each group are the same), we have:
\[
SE = \sqrt{\frac{0.0}{16} + \frac{0.0}{16}} = 0.0
\]
Step 2: Test Statistic Calculation
The test statistic \( t \) is calculated using the formula:
\[
t = \frac{\bar{x}_1 - \bar{x}_2}{SE}
\]
Substituting the sample means and the standard error:
\[
t = \frac{5.75 - 5.0}{0.0} = \infty
\]
Step 3: Degrees of Freedom Calculation
The degrees of freedom \( df \) for Welch's t-test is calculated using the formula: