Please respond to the following questions either by writing the design name or by describing the design using standard notation (X = program, O=observation, R= random assignment). For each design, please discuss all threats to internal validity.
1. a. Design: Single group post-test only
b. Internal validity threats:
2. a. Design: (R) O1 X O2
(R) O1 O2
b. Internal validity threats:
3. a. Design: Pretest-posttest design with experimental and comparison group
b. Internal validity threats:
4. a. Design: O X O
b. Internal validity threats:
5. a. Design: Single group with three pretests and four posttests
b. Internal validity threats:
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1. The design is a single group post-test only design. In this design, there is only one group and the outcome is measured after the intervention.
Some threats to internal validity in this design include:
- History: Changes in the outcome may be due to external factors or events that occur between the intervention and the post-test measurement.
- Maturation: Changes in the outcome may be due to natural development or maturation of the participants over time.
- Testing: Participants may become more familiar with the outcome measurement procedure and perform better on subsequent measurements due to practice or learning effects.
- Instrumentation: Changes in the outcome may be due to changes in the measurement instrument or procedure used.
- Regression to the mean: Extreme scores obtained on the pre-test may move closer to the group mean on the post-test due to chance.
2. The design is a randomized controlled trial (RCT) with two groups: an experimental group exposed to an intervention (X) and a comparison group not exposed to the intervention. Each group is measured twice, once before the intervention (O1) and once after the intervention (O2).
Some threats to internal validity in this design include:
- Selection bias: Random assignment may not result in equivalent groups, leading to systematic group differences at baseline.
- Attrition/mortality: Participants may drop out or be lost to follow-up in one or both groups, introducing bias if the missing data are related to the outcome.
- Diffusion of treatment: Information or intervention between groups may be shared, contaminating the comparison group.
- Interaction between selection and treatment: The effect of the intervention may vary depending on participant characteristics or group assignment.
- Hawthorne effect: Participants may change their behavior simply because they are being observed or receiving attention.
3. The design is a pretest-posttest design with an experimental group that receives an intervention and a comparison group that does not receive the intervention.
Some threats to internal validity in this design include:
- Selection bias: Nonrandom assignment to groups may result in systematic group differences at baseline.
- Attrition/mortality: Participants may drop out or be lost to follow-up in one or both groups, introducing bias if the missing data are related to the outcome.
- Regression to the mean: Extreme scores obtained on the pre-test may move closer to the group mean on the post-test due to chance.
- History: Changes in the outcome may be due to external factors or events that occur between the pre-test and post-test measurements.
- Maturation: Changes in the outcome may be due to natural development or maturation of the participants over time.
4. The design is a simple pretest-posttest design with one group. The outcome is measured before the intervention (O1), then the intervention is administered (X), and the outcome is measured again after the intervention (O2).
Some threats to internal validity in this design include:
- History: Changes in the outcome may be due to external factors or events that occur between the pre-test and post-test measurements.
- Maturation: Changes in the outcome may be due to natural development or maturation of the participants over time.
- Testing: Participants may become more familiar with the outcome measurement procedure and perform better on the post-test due to practice or learning effects.
- Instrumentation: Changes in the outcome may be due to changes in the measurement instrument or procedure used.
- Regression to the mean: Extreme scores obtained on the pre-test may move closer to the individual's true score on the post-test due to chance.
5. The design is a single group design with three pretests and four posttests. The outcome is measured multiple times before and after the intervention.
Some threats to internal validity in this design include:
- History: Changes in the outcome may be due to external factors or events that occur between the pretests and posttests.
- Maturation: Changes in the outcome may be due to natural development or maturation of the participants over time.
- Testing: Participants may become more familiar with the outcome measurement procedure and perform better on subsequent measurements due to practice or learning effects.
- Instrumentation: Changes in the outcome may be due to changes in the measurement instrument or procedure used.
- Regression to the mean: Extreme scores obtained on the pretests may move closer to the individual's true score on the posttests due to chance.