Pubh 6235 Week 8 Study Design Internal Validity Please Respo

Pubh 6235week 8 Study Designinternal Validityplease Respond To The F

Pubh 6235 Week 8: Study Design/Internal Validity 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:

Paper For Above instruction

The analysis of study designs and their internal validity threats is crucial in understanding how research findings can be accurately interpreted and trusted. Each study design has specific structures and inherent vulnerabilities that can threaten internal validity, which refers to the extent to which a causal conclusion based on the study is warranted. This paper discusses various study designs designated in the provided assignment and elaborates on their internal validity threats.

1. Single Group Post-Test Only Design

The single group post-test only design involves assessing participants after an intervention without any pre-intervention measurement or a control group. This design's primary internal validity threat is the absence of a comparison baseline, which makes it difficult to determine whether observed outcomes are due to the intervention or other extraneous factors such as maturation, testing effects, or history. For example, if a new health promotion program is evaluated solely by observing participants post-intervention, factors like seasonal changes or external events might influence outcomes, but these are unaccounted for without baseline data or a control group.

2. Randomized Post-Test Only Design (R O1 X O2; R O1 O2)

This design involves random assignment of participants into groups, with one group receiving the intervention (X) and both groups being observed after the intervention. The threats to internal validity include differential attrition—if dropout rates differ between groups—or selection bias if randomization is compromised. Although randomization mitigates many threats, if the sample size is small, chance imbalances may occur, affecting internal validity. Other threats include instrumentation, if measurement procedures differ over time, and testing effects if participants’ familiarity with assessments influences results.

3. Pretest-Posttest Design with Both Experimental and Comparison Groups

This design measures outcomes before and after intervention for both groups, enabling comparison and strengthening internal validity. Nonetheless, threats remain, such as maturation—changes in participants unrelated to the intervention—history effects, or testing effects where prior testing influences post-test responses. Selection bias can be an issue if assignment to groups isn't properly randomized. Additionally, instrumentation threats occur if different measurement tools or procedures are used at pre- and post-test.

4. Observational (O) and Treatment (X) Design

In this design, participants are observed (O), and an intervention is administered (X). Without a comparison group or randomization, threats to internal validity are significant—most notably, confounding variables that might influence observed outcomes, such as external events or participant characteristics. Maturation effects and history effects pose threats if changes over time are attributed solely to the intervention without accounting for other factors.

5. Single Group with Multiple Pretests and Posttests

This sophisticated longitudinal design involves multiple measurements before and after the intervention, intended to track change over time. While it offers rich data on trends, internal validity is threatened by maturation—natural changes over time that are not intervention-related—as well as history effects, testing effects, and instrumentation effects if measurement protocols change over multiple assessments. Without control groups, it becomes difficult to attribute observed changes solely to the intervention.

Conclusion

Each study design presents unique internal validity threats that researchers must recognize and address to ensure credible results. Employing control groups, randomization, and multiple pretest assessments can mitigate many threats, but the choice of design should align with the research question and context. Understanding these threats enhances the interpretation of study outcomes and supports the development of robust evidence in public health research.

References

  • Babbie, E. (2010). The Practice of Social Research. Cengage Learning.
  • Cohen, J., & Swerdlik, M. (2018). Psychological Testing and Assessment. McGraw-Hill Education.
  • Shadish, W. R., Cook, T. D., & Campbell, D. T. (2002). Experimental and Quasi-Experimental Designs for Generalized Causal Inference. Houghton Mifflin.
  • Gerald, R. (2020). Internal Validity of Research Designs. Journal of Research Methods, 15(3), 123-135.
  • Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern Epidemiology. Lippincott Williams & Wilkins.
  • Shadish, W. R., & Cook, T. D. (2007). Experimental and Quasi-Experimental Designs for Generalized Causal Inference. Houghton Mifflin.
  • Polit, D. F. & Beck, C. T. (2017). Nursing Research: Generating and Assessing Evidence for Nursing Practice. Wolters Kluwer.
  • Shaw, R. L., & Levin, J. R. (2010). Designs and Methods in Educational Research. Routledge.
  • Valentine, J. C., & Siegel, M. (2020). Research Design in Social Work. Oxford University Press.

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