Russel-Research-Method-in-Anthropology

Research Design: Experiments and Experimental Thinking 119
Time 1 Time 2
Assignment Pretest Intervention Posttest
Group 1 R O1
X O
Group 2 R O O
a.
The Classic Design: Two-Group Pretest-Posttest
Group 1 R O1
X O
Group 2 R O3
O
Group 3 R X O
Group 4 R O
b.
The Solomon Four-Group Design
3
2
4
2
4
5
6
Group 1 O X
Group 2 O
c.
The Classic Design Without Randomization
1
3
O
O
2
4
Group 1 R X O
Group 2 R O
d.
The Campbell and Stanley Posttest-Only Design
1
2
e.
The One-Shot Case Study Design
X
O
f.
O 1 X
The One-Group Pretest-Posttest Design
X O
O
2
g.
Two-Group Posttest Only: Static Group Comparison Design
O
1
2
OOO
X
h.
The Interrupted Time Series Design
Figure 5.1. Some research designs.
O O O
experiment. Later, at time 2, after the first group has been exposed to the intervention,
the second group is observed again. That’s O 4 .
Random assignment of participants ensures equivalent groups, and the second
group, without the intervention, ensures that several threats to internal
validity are taken care of. Most importantly, you can tell how often (how
many times out of a hundred, for example) any differences between the pretest