Which of these scenarios means that a pretest-posttest design with a non-equivalent control group is not suitable? Select all that apply.
a. All of the available participants will be receiving the intervention at the same time.
b. Authors want to examine for any trends in the data over time.
c. The participants were placed into the experimental and control groups by natural circumstances rather than random assignment.
d. Authors want to compare averages between two groups before and after the intervention using an ANOVA.
The correct answer and explanation is :
Correct answers:
- a. All of the available participants will be receiving the intervention at the same time.
- b. Authors want to examine for any trends in the data over time.
Explanation (≈300 words):
A pretest-posttest design with a non-equivalent control group is a quasi-experimental design commonly used when random assignment isn’t possible. It involves measuring outcomes in two groups—one receiving the intervention and one not—both before and after the intervention. However, there are certain conditions where this design is not suitable:
a. All of the available participants will be receiving the intervention at the same time
✅ Unsuitable.
This violates a key requirement of the design: having a control group that does not receive the intervention. Without a comparison group, it’s impossible to isolate the effect of the intervention from other confounding variables, such as time or environment. This scenario would be more appropriate for a single-group pretest-posttest or time-series design, though both have weaker internal validity.
b. Authors want to examine for any trends in the data over time
✅ Unsuitable.
The non-equivalent control group design is typically structured for pre- and post-intervention comparisons, not for identifying longitudinal trends or changes across multiple time points. For trend analysis, a time-series design (e.g., interrupted time series) is more suitable as it collects multiple observations before and after the intervention, allowing for the detection of patterns over time.
c. The participants were placed into the experimental and control groups by natural circumstances rather than random assignment
❌ Suitable.
This is a defining feature of the non-equivalent control group design. Random assignment is not required; the groups are formed based on existing conditions, which is why the design is considered quasi-experimental.
d. Authors want to compare averages between two groups before and after the intervention using an ANOVA
❌ Suitable.
ANOVA is a common statistical method for analyzing group mean differences. It’s appropriate for this design, assuming assumptions are met (e.g., homogeneity of variance).