Experiments. Pre and Post condition. Classic experimental design. Random assignment to control and treatment conditions Why random assignment and control groups?. Classic experimental design. Random assignment helps with internal validity Some threats to internal validity:
Pre and Post condition
t2 = F
Including a pretest can sensitize participants and create a threat to construct validity. Combining the two basic designs creates the Solomon 4-group design, which can determine if pretest sensitization is a problem:
R X O
R O X O
R O O
If these two groups are different, pretest sensitization is an issue.
If these two groups are different, there is a testing effect.
*A two-tailed probability is given for zmeta