Russel-Research-Method-in-Anthropology

Research Design: Experiments and Experimental Thinking 123
conditions in the experiment. Then, the confound would disappear—not
because land holding stops being a factor in how well women respond to the
opportunity to get agricultural credits, but because women who have varying
amounts of land would be equally likely to be in the treatment group or in the
control group. Any bias that the amount of land causes in interpreting the
results of the experiment would be distributed randomly and would be equally
distributed across the groups.
But people come packaged in villages, and you can’t give just some women
in a small village instruction about applying for credit and not give it to others.
So evaluation of these kinds of interventions are usually quasi-experiments
because they have to be.
The Posttest-Only Design with Random Assignment
Look carefully at figure 5.1d. It is the second half of the Solomon fourgroup
design and is called the Campbell and Stanley posttest-only design.
Time 1 Time 2
Assignment Pretest
Intervention Posttest
Group 1 R X O 1
2
Group 2
R
O
Figure 5.1d. The Campbell and Stanley posttest-only design.
This design has a lot going for it. It retains the random assignment of participants
in the classical design and in the Solomon four-group design, but it eliminates
pretesting—and the possibility of a confound from pretest sensitization.
When participants are assigned randomly to experimental conditions (control
or treatment group), a significant difference between O 1 and O 2 in the posttestonly
design means that we can have a lot of confidence that the intervention,
X, caused that difference (Cook and Campbell 1979).
Another advantage is the huge saving in time and money. There are no pretests
in this design and there are only two posttests instead of the four in the
Solomon four-group design.
Here’s an example of this elegant design. McDonald and Bridge (1991)
asked 160 female nurses to read an information packet about a surgery patient
whom they would be attending within the next 8 hours. The nurses were
assigned randomly to one of eight experimental conditions: (1) The patient
was named Mary B. or Robert B. This produced two patient-gender condi-