A study tested whether a new drug had an effect (positive or
negative) on short-term memory in Alzheimer patients. They
gathered a sample of 6 male and 6 female Alzheimer patients
in their seventies from the SD area. Subjects were randomly
assigned to either placebo or drug conditions with 3 males
and 3 females in each condition. All subjects took a pill
early in the morning for one month. The pill contained
150mg of the drug in the experimental group and a neutral
substance for the control group. After 1 month of treatment
subjects were tested using a standard memory test (the larger
the score, the better). The lab assistant tested all male
subjects in the morning and female subjects in the afternoon.
Table 1 shows the results obtained with the 12 subjects.
![tabular34](img4.gif)
We can think of the experiment as consisting of four groups:
Female Drug as Group 1, Female Placebo as Group 2, Male
Drug as Group 3, and Male Placebo as Group 4.
- For each possible intervening variable, state how it was
controlled or if it were not controlled:
- Differences between males and females in memory?
- Differences of different individuals in memory?
- Differences due to how much drug was taken?
- Differences due to the time of day the test was taken?
-
Compute the sample mean and variance for each group.
-
Compute the pooled estimate of variance. How many degrees
of freedom does it have?
-
Do we have enough evidence to say the drug has an effect
on women?
-
Do we have enough evidence to say the drug has an effect
on men?
-
Find the 95 % confidence intervals of each of the 4 group means.
-
Let
represent the effect of the drug in females,
and let
represent the effect in males. Do you
have enough evidence to say the drug has an interaction, that
is that it has a different effect in males than it does in females?