Hybrid Experimental Designs
Hybrid Designs



Variations on randomized designs
Help to address specific threats
Incorporates different design features
Two will be illustrated here.
The Solomon Four-Group Design
R
R
R
R


O
O
X
X
O
O
O
O
Explicitly addresses a testing threat
Assesses the effect of taking a pretest
Possible Outcomes
Treatment Effect -- No Testing Effect
18
16
14
Tpre-post
Cpre-post
Tpost
Cpost
12
10
8
6
Pre
Post
Possible Outcomes
Treatment Effect and Testing Effect
18
16
14
Tpre-post
Cpre-post
Tpost
Cpost
12
10
8
6
Pre
Post
Switching Replications Design
R
R


O
O
X
O
O
X
O
O
Switching: the groups switch roles over
the course of the study.
Replications: the treatment is repeated
or replicated.
Possible Outcomes
Short-term Persistent Treatment Effect
18
16
14
Group 1
Group 2
12
10
8
6
Pre
Post1
Post2
Possible Outcomes
Long-term Continuing Treatment Effect
18
16
14
Group 1
Group 2
12
10
8
6
Pre
Post1
Post2
Switching Replications




Very strong in internal validity
Looks at short and longer term effects
Strong ethically because all participants
get the treatment
Works well with some institutional
structures (for example, semester
system in schools)