When groups are not equivalent because of pre-existing differences, the study suffers from what?

When groups are not equivalent because of pre-existing differences, the study suffers from what?

• A. Non-equivalent groups
• B. Participant variables
• C. Baseline measure
• D. Debriefing

Answer: (A)

Main concept: when groups differ from the start because of pre-existing differences, the study’s internal validity is compromised. This situation is described as non-equivalent groups, a hallmark of quasi-experimental designs where random assignment isn’t used. Those pre-existing differences can confound the results, making it unclear whether outcomes are due to the manipulated variable or to baseline disparities. Baseline measures are used to check how similar groups are before the intervention, but they don’t by themselves fix the issue. Debriefing is simply informing participants after the study and isn’t about group equivalence. While participant variables describe the kinds of pre-existing differences, the best label for the design problem is non-equivalent groups.

Main concept: when groups differ from the start because of pre-existing differences, the study’s internal validity is compromised. This situation is described as non-equivalent groups, a hallmark of quasi-experimental designs where random assignment isn’t used. Those pre-existing differences can confound the results, making it unclear whether outcomes are due to the manipulated variable or to baseline disparities. Baseline measures are used to check how similar groups are before the intervention, but they don’t by themselves fix the issue. Debriefing is simply informing participants after the study and isn’t about group equivalence. While participant variables describe the kinds of pre-existing differences, the best label for the design problem is non-equivalent groups.