Assignment
1. In a psychology experiment, 80 subjects were randomly assigned to either a control or an
experimental group. After the experiment, some subjects from each group had dropped
out and the following data were obtained:
Control Group Experimental Group
nC = 38 nE = 34
XC = 75 XE = 80
SC = 14.5 SE = 16.2
a) Test the research hypothesis that the sample means are significantly different from one
another (α ≤ .05).
b) If XC is still equal to 75, and both groups' sample sizes and standard deviations remain
unchanged, at least how high would XE have to be to be considered significantly higher
than XC (α ≤ .05)?
c) Suppose both groups' means and standard deviations are unchanged but nC is now 12
and nE is 8. Is XE significantly higher than XC (α ≤ .01)?
2. Subjects were randomly assigned to one of two treatment conditions in a medical
research project which was investigating the effect of a new drug which was expected to
lower the resting pulse rates of people with high blood pressure. Subjects in group 1
were administered the new drug, while subjects in group 2 were given a placebo. One
hour later, the subjects' resting pulse rates were measured, yielding the following results:
Group 1 Group 2
n1 = 13 n2 = 16
X1 = 78.4 X2 = 85.8
S1 = 10.73 S2 = 8.62
a) Perform the appropriate statistical procedure(s) to determine whether the new drug
was effective (α ≤ .05).
b) The mean resting pulse rate of the population of people who do not suffer from high
blood pressure is 72.8. Is group 1's mean significantly different from this (α ≤ .01)?
(Hint: think back to last term...)
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