Chapter 8

Question 1

IN THE EXPERIMENTAL METHOD, THE RESEARCHER ATTEMPTS TO CONTROL

Answer 1

ALL EXTRANEOUS VARIABLES.

Question 2

The simplest possible experimental design has two variables:

Answer 2

the independent variable and the dependent
variable. The independent variable has a minimum of two levels, an experimental group and a control group. Researchers must make every effort to ensure that the only difference between the two groups is the
manipulated (independent) variable.

Question 3

The basic, simple experimental design can take one of two forms

Answer 3

a posttest-only design or a pretest-posttest design.

Question 4

posttest-only design must

Answer 4

all of these:

1) obtain two equivalent groups of participants
2) manipulate the independent variable
3) measure the effect of the independent variable on the dependent variable.

Question 5

posttest-only design

Answer 5

A true experimental design in which the dependent variable (posttest) is measured only once, after manipulation of the independent variable.

Question 6

selection differences

Answer 6

Differences in the type of subjects who make up each group in an experimental design. One way such differences can arise is by allowing participants to choose which group they will be assigned to.

Question 7

pretest-posttest design

Answer 7

A true experimental design in which the dependent variable is measured both before (pretest) and after (posttest) manipulation of the independent variable. This design makes it possible to ascertain that the groups were, in fact, equivalent at the beginning of the
experiment. However, this precaution is usually not necessary if participants have been randomly assigned to the two groups. With a sufficiently large sample of participants, random assignment will produce groups that are virtually identical in all respects.

Question 8

Advantages of pretest

Answer 8

All of these:
1) a pretest enables the researcher to tell whether the groups are in fact equivalent to begin with.
2) The pretest-posttest design immediately makes us focus on the change from pretest to posttest. This
emphasis on change is incorporated into the analysis of the group differences. Also, the extent of change in
each individual can be examined.
3) A pretest is also useful whenever there is a possibility that participants will drop out of the experiment; this is most likely to occur in a study that lasts over a long time period.

Question 9

attrition or mortality

Answer 9

The loss of subjects who decide to leave an experiment. Mortality is a threat to internal validity when the mortality rate is related to the nature of the experimental manipulation.

Question 10

Disadvantage of pretest

Answer 10

time-consuming and awkward to administer in
the context of the particular experimental procedures being used. Perhaps most important, a pretest can
sensitize participants to what you are studying, enabling them to figure out what is being studied and
(potentially) why. They may then react differently to the manipulation than they would have without the
pretest. When a pretest affects the way participants react to the manipulation, it is very difficult to generalize the results to people who have not received a pretest. That is, the independent variable may not have an effect in the real world, where pretests are rarely given.

Question 11

if awareness of the pretest is a problem, the pretest can be

Answer 11

disguised. One way to do this is by administering it in a completely different situation with a different experimenter. Another approach is to embed the pretest in a set of irrelevant measures so it is not obvious that the researcher is interested in a
particular topic.

Question 12

It is possible to assess the impact of the pretest directly with a combination of both the posttest-only
and the pretest-posttest design. In this design, half the participants receive only the posttest, and the other
half receive

Answer 12

both the pretest and the posttest. This is formally called a Solomon four-group design.

Question 13

If there is no impact of the pretest, the posttest scores will be

Answer 13

the same in the two control groups (with and

without the pretest) and in the two experimental groups

Question 14

independent groups design

Answer 14

An experiment in which different subjects are assigned to each group. Also called between-subjects design.

Question 15

within-subjects design

Answer 15

An experiment in which the same subjects are assigned to each group. Also called repeated measures design.

Question 16

random assignment

Answer 16

Use of a random “chance” procedure (such as a random number generator or coin toss) to determine which condition an individual will participate in.

Question 17

The repeated measures design has several advantages

Answer 17

All of these:
1) fewer research participants are needed, because
each individual participates in all conditions. When participants are scarce or when it is costly to run each
individual in the experiment, a repeated measures design may be preferred. In much research on perception, for instance, extensive training of participants is necessary before the actual experiment can begin. Such research often involves only a few individuals, who participate in all conditions of the experiment.
2) they are extremely sensitive to finding statistically significant differences between groups. This is because we have data from the same people in both
conditions.

Question 18

The major problem with a repeated measures design stems from the fact that the different conditions must
be presented in a

Answer 18

particular sequence

Question 19

order effect

Answer 19

In a repeated measures design, the effect that the order of introducing treatment has on the dependent variable.

Question 20

practice effect or learning effect

Answer 20

Improvement in participant performance with repeated testing.

Question 21

fatigue effect

Answer 21

Deterioration in participant performance with repeated testing.

Question 22

carryover effect

Answer 22

A problem that may occur in repeated measures designs if the effects of one treatment are still present when the next treatment is given.

Question 23

There are two approaches to dealing with order effects

Answer 23

The first is to employ counterbalancing techniques. The second is to devise a procedure in which the interval between conditions is long enough to minimize the influence of the first condition on the second.

Question 24

counterbalancing

Answer 24

A method of controlling for order effects in a repeated measures design by either including all orders of treatment presentation or randomly determining the order for each subject.

Question 25

Counterbalancing principles can be extended to experiments with

Answer 25

three or more groups. With three groups, there are 6 possible orders (3! = 3 × 2 × 1 = 6). With four groups, the number of possible orders increases to 24 (4! = 4 × 3 × 2 × 1 = 24); you would need a minimum of 24 participants to represent each order, and you would need 48 participants to have only two participants per order.

Question 26

Latin square

Answer 26

A technique to control for order effects without having all possible orders.

Question 27

to construct a Latin square

Answer 27

a limited set of orders constructed to ensure that
1) each condition appears at each ordinal
position, and
2) each condition precedes and follows each condition one time.

Question 28

A rest period may counteract a

Answer 28

fatigue effect. Attending to an unrelated task
between treatments may reduce the possibility that participants will contrast the first treatment with the
second. If the treatment is the administration of a drug that takes time to wear off, the interval between
treatments may have to be a day or more.

Question 29

A very different consideration in whether to use a repeated measures design concerns generalization to
conditions in the “real world.”

Answer 29

in actual everyday situations, we sometimes encounter independent variables in an independent groups fashion: We encounter only one condition without a contrasting comparison. However, some independent variables are most frequently encountered in a repeated measures fashion: Both conditions appear, and our responses occur in the context of
exposure to both levels of the independent variable. Thus, for example, if you are interested in how a
defendant’s characteristics affects jurors, an independent groups design may be most appropriate because actual jurors focus on a single defendant in a trial. However, if you are interested in the effects of a job applicant’s characteristics on employers, a repeated measures design would be reasonable because employers typically consider several applicants at once. Whether to use an independent groups or repeated measures design may be partially determined by these generalization issues.

Question 30

any experimental procedure that produces a relatively permanent change in an individual cannot be used in a

Answer 30

repeated measures design. Examples include a psychotherapy treatment or a surgical procedure
such as the removal of brain tissue.

Question 31

matched pairs design

Answer 31

A method of assigning subjects to groups in which pairs of subjects are first matched on some characteristic and then individually assigned randomly to groups