Social Research Methods: Qualitative and Quantitative Approaches

EXPERIMENTAL RESEARCH

We use these preexperimental designsin situa-
tions in which it is difficult to use the classical
design. The designs have weaknesses that make
inferring a causal relationship difficult.

One-Shot Case-Study Design. Also called the
one-group posttest-only design,the one-shot case-
study designhas only one group, a treatment, and
a posttest. Because there is only one group, there is
no random assignment.

Example. You take a group of forty newly hired
waitstaff and give all a 2-hour training session
in which you instruct them to introduce themselves
to customers by first name and to check on the cus-
tomers, asking, “Is everything fine?” 8 to 10 min-
utes after delivering the food (treatment). The
participants begin employment, and you record the
amount in tips for all for one month (posttest score).

One-Group Pretest-Posttest Design. This design
has one group, a pretest, a treatment, and a posttest.
It lacks a control group and random assignment.

Example. You take a group of forty newly hired
wait staff and give all a 2-hour training session. You
instruct the staff members to follow a script in
which they are not to introduce themselves by first
name and not to return during the meal to check on
the customers. All begin employment, and you
record the amount in tips for all for one month
(pretest score). Next, you “retrain” all 40 partici-
pants and instruct them henceforth to introduce
themselves to customers by first name and to check
on the customers, asking, “Is everything fine?” 8
to 10 minutes after delivering the food (treatment).
Over the second month, you record the amount of
tips for both groups (posttest score).
This is an improvement over the one-shot case
study because you measure the dependent variable
before and after the treatment. But it lacks a control
group. We cannot know whether something other
than the treatment occurred between the pretest and
the posttest to cause the outcome.

Static Group Comparison. Also called the
posttest-only nonequivalent group design,a static
group comparisonhas two groups, a posttest, and
treatment. It lacks random assignment and a

pretest. A weakness is that any posttest outcome

difference between the groups could be due to

group differences prior to the experiment instead

of to the treatment.

Example. You give forty newly hired waitstaff an

identical 2-hour training session and instruct all to

follow a script in which servers are not to introduce

themselves by first name and but to return during

the meal to check on the customers. They can choose

one of the two restaurants at which to work, as long

as each restaurant has twenty people. All begin em-

ployment. After one month, you “retrain” the twenty

participants at restaurant 1 (experimental group) and

instruct them henceforth to introduce themselves to

customers by first name and to check on the cus-

tomers, asking, “Is everything fine?” 8 to 10 min-

utes after delivering the food (treatment). The group

at restaurant 2 (control group) is “retrained” to con-

tinue without an introduction or checking during

the meal. Over the second month, you record the

amount of tips for both groups (posttest score).

Quasi-Experimental and Special Designs.These

designs, like the classical design, make identifying

a causal relationship more certain than do pre-

experimental designs. Quasi-experimental de-

signs help us test for causal relationships in

situations in which the classical design is difficult

or inappropriate. We call them quasibecause they

Preexperimental designs Experimental plans that

lack random assignment or use shortcuts and are much

weaker than the classical experimental design; are

substituted in situations in which an experimenter can-

not use all of the features of a classical experimental

design but the design has weaker internal validity.

Static group comparison design An experimental

plan with two groups, no random assignment, and only

a posttest.

Quasi-experimental designs Plans that are stronger

than preexperimental ones; variations on the classical

experimental design used in special situations or when

an experimenter has limited control over the inde-

pendent variable.

One-shot case-study design An experimental plan

with only an experimental group and a posttest but no

pretest.