PSY 555 Homework 12
Answers
Chapter 8: #1,3,7,8,9,15
8.1(a). d=
8.1(b). The
function of n for a one-sample t-test is equal to 
.
8.1(c). Power=.71.
8.3(a). For power=.70, 
Round
up because you cannot have 99 participants.
So,
you would need 99 participants to have a power of .70.
8.3(b). For power=.80, 
So,
you would need 126 participants to have a power of .80.
8.3(c). For power=.90, 
So,
you would need 169 participants to have a power of .90.
8.7(a). d=
For
power=.5, 
You
would need 16 participants to have a power of .50.
8.7(b). For
power=.80,
You
would need 32 participants to achieve a power of .80.
8.8(a). For
power=.60, 
78
participants (39 in each group) would be needed to achieve a power of .60.
8.8(b). For
power=.90,
170
participants (85 in each group) would be needed to achieve a power of .90.
8.9. d=.5
N=15+20=35
The
power of this experiment is .29.
8.15. 
High School
Dropouts Delinquent
Graduates
N=50 
He
should use the high school dropout group because that group will produce the
highest power.
1. Alpha
is the probability of rejecting the null hypothesis when the null hypothesis is
true (the probability of making a Type I error). Beta is the probability of failing to reject
the null hypothesis when the null hypothesis is false (the probability of a
Type II error). Power is the probability
of finding an effect given there is an effect to be found (e.g., rejecting the
null hypothesis when you should have rejected the null hypothesis; defined as 1-b).
2. You can increase power by:
1) increasing sample
size (N),
2) creating a larger
effect size (by increasing the experimental manipulation—e.g., raise the drug
dose of an experimental group to a higher level to compare to a control),
3) use a more sensitive statistical test,
4) adjust the alpha
level (specifically, increase alpha level; e.g., .05 moves to .10), or
5)
increasing the sensitivity of the measure (e.g.,
measure in inches rather than yards).
3). 
s=3
.05
z=1.64
Z=
