Statistical Methods for Psychology
For each of the hypothesis testing problems below, you need to justify your answer by explicitly
defining your null hypothesis H0 and alternative hypothesis H1 and reporting the p-value for the
resulting test statistic.
1. Two separate samples receive two different treatments. The first treatment group (N = 9)
has a mean of 50 with SS = 710. The second treatment group (N = 6) has a mean of 60
with SS = 460. Is the second treatment group significantly larger than the first? What is
the effect size?
2. A researcher surveys a group of college students to determine the negative life events that
they experienced in the past 5 years and their current feeling of well-being. For N = 18
participants with 2 or fewer negative experiences, the average well-being score was X = 42
with SS = 398. For the N = 16 participants with 5 to 10 negative experiences the average
score is X = 48.6 with SS = 370. Is there a significant difference between the two populations
represented by these two samples? What is the effect size?
3. In 1974, Loftus and Palmer conducted a classic study demonstrating how the language used
to ask a question can influence eyewitness memory. In the study, college students watched a
film of an automobile accident and then they were asked questions about what they saw.
One group was asked “About how fast were the cars going when they smashed into each other?”
Another group was asked the same question except the verb was changed to “hit” instead of
“smashed into”. The “smashed into” group reported significantly higher estimates of speed
than the “hit” group.
Suppose a researcher repeats the study with a sample of today’s college students and obtains the following results:
Smashed into Hit
n = 15 n = 15
M = 40.8 M = 34.0
SS = 510 SS = 414
Do the results indicate a significantly higher estimated speed for the “smashed into” group?
What is the effect size?