Statistics for the Behavioral Sciences by Frederick J. Gravetter, Larry B. Wallnau ISBN 10: 1305504917 ISBN 13: 9781305504912

302 CHAPTER 10 | The t Test for Two Independent Samples
LEARNING CHECK
1. Which of the following describes an independent-measures research study?
a. Two separate samples are used to obtain two groups of scores to represent the
two populations or two treatment conditions being compared.
b. The same group of participants is measured in two treatment conditions to obtain
two groups of scores.
c. One group of participants is used to obtain one group of scores.
d. None of the above is an accurate description
2. Which of the following is an example of an independent-measures design?
a. Comparing performance scores for 6-year-old boys and 6-year-old girls.
b. Comparing depression scores before and after therapy.
c. Measuring weekend wake-up times for a group of adolescents.
d. Measuring smoking behavior immediately after a group of participants
completes a stop-smoking program and measuring them again six months
later.
3. A repeated-measures study comparing two treatment conditions uses ___ group(s)
of participants and obtains ___ score(s) for each participant.
a. 1, 1
b. 1, 2
c. 2, 1
d. 2, 2
ANSWERS
1. A, 2. A, 3. B
10.2 The Null Hypothesis and the Independent-Measures
t Statistic
LEARNING OBJECTIVES
2. Describe the hypotheses for an independent-measures t test.
3. Describe the structure of the independent-measures t statistic and explain how it is
related to the single-sample t.
4. Calculate the estimated standard error for a sample mean difference,
s (M1
, including the pooled variance, which is part of the equation.
2M 2
)
5. Calculate the complete independent-measures t statistic and its degrees
of freedom.
Because an independent-measures study involves two separate samples, we need some special
notation to help specify which data go with which sample. This notation involves the
use of subscripts, which are small numbers written beside a sample statistic. For example,
the number of scores in the first sample would be identified by n 1
; for the second sample,
the number of scores is n 2
. The sample means would be identified by M 1
and M 2
. The sums
of squares would be SS 1
and SS 2
.