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:

1. Design: Single group post-test only

a. Internal validity threats: In this design, there are several threats to internal validity, such as history, maturation, testing, and regression to the mean. For example, changes in the outcome may be attributed to events that occur between the pretest and post-test or natural developmental or maturation processes rather than the treatment itself. Additionally, the act of taking the pretest may influence participants' responses on the post-test, leading to testing effects.

2. Design: (R) O1 X O2
(R) O1 O2

a. Internal validity threats: In this design, the main threat to internal validity is selection bias. If the random assignment is not effectively implemented, there might be differences between the two groups at the beginning of the study, affecting the internal validity. Additionally, there could be threats from history or maturation if there are external events or natural developmental processes that occur between the two observations that could influence the outcome.

3. Design: Pretest-posttest design with experimental and comparison group

a. Internal validity threats: In this design, besides the threats mentioned in the previous designs (history, maturation, testing, and regression to the mean), there is also a threat known as selection bias. If the groups are not equivalent at the beginning of the study, any differences found between the groups post-treatment cannot be confidently attributed to the treatment itself. Other threats include attrition, where there may be differential dropout rates between the groups, and diffusion or contamination, where treatment effects may spill over from the experimental group to the comparison group or vice versa.

4. Design: O X O

a. Internal validity threats: In this design, the main threat to internal validity is history. Any external events or changes that occur between the pretest and post-test may influence the outcome measure, making it difficult to determine if the treatment itself caused the observed changes. Other threats include maturation, testing, and regression to the mean, as mentioned in the previous designs.

5. Design: Single group with three pretests and four posttests

a. Internal validity threats: In this design, the primary threat to internal validity is maturation. The repeated measurements over time may capture natural developmental processes that occur independent of the treatment. Additionally, there could be testing effects, as participants become more familiar with the tests and improve their performance over time. History can also be a threat if there are external events occurring during the study that could influence the outcome.