Final answer:
A non-equivalent control group design with pretest and posttest is a quasi-experimental design where groups are not randomly assigned and changes in the dependent variable are measured before and after treatment.
Interpretable results can be obtained when other factors are controlled for, and changes are significantly different from those in the control group, suggesting that the treatment is effective.
Step-by-step explanation:
A non-equivalent control group design with pretest and posttest is a type of quasi-experimental design where participants are not randomly assigned to treatment and control groups.
Instead, groups are pre-existing, which means they may differ in important ways unrelated to the treatment. Participants in both groups are tested on the key variable before (pretest) and after (posttest) the treatment occurs
Results of quasi-experiments using this design are interpretable under certain circumstances, such as when researchers can confidently establish that the changes in the dependent variable are due to the treatment rather than other factors.
This could involve statistical adjustments, comparison with historical trends, or replication of findings across different non-equivalent groups.
The measurable change from pretest to posttest can offer insight into the treatment's effectiveness, especially when changes in the treatment group are significantly different from those in the control group, and alternative explanations for these changes can be ruled out.
Ensuring the integrity of the experimental design includes having a control group that does not receive the active treatment but instead may receive a placebo, allowing for a comparison of effects between the groups.
Ideally, the people scoring the outcomes of the pretest and posttest should be blind to the group assignments to avoid experimenter bias.