Study Design and Internal Validity

Part I. Read the following scenarios, and answer the questions in essay style. Hint: each scenario has a different threat to internal validity.

1.Em is interested in examining how changes in income (IV) affect health later in life (DV). She has access to a rich, longitudinal dataset, in which participants answered questionnaires every 10 years from ages 18 to 78 years. She is ready to do her analyses but notices that the first three surveys asked about participant’s yearly income (i.e., participant only) whereas the last four surveys asked about total family income (i.e., participant’s income plus any other household member’s income). Thus, her measure of income differs across time. What type of threat to internal validity did Em discover? State and explain how this is a threat in relation to the DV. What could the original researchers who designed the study have done to protect against this threat to internal validity?

2. Ezequiel is interested in examining whether exercise (IV) improves memory (DV). He reads a list of words to participants, has them take a 5-minute break, and then has them repeat the list of words back to him. Following this, he has participants complete 30 minutes of cardiovascular exercise. Afterwards, he reads them the same list of words, and after a 5-minute break, has them repeat the list back to him. He is very excited because his hypothesis was supported: people remember more words AFTER 30 minutes of exercise. However, there is a problem with his design. What type of threat to internal validity plagues his study? State and explain how this is a threat in relation to the DV. What can Ezequiel do the next time he runs his experiment to protect against this threat to internal validity?

3. Amy is conducting an experiment to test whether a new learning method (IV) will improve the test scores (DV) of Public Health students. She learned in her research class that she should have a control group, so she decides to implement her new learning method in one class she is teaching but not the other. The experimental group with whom she is piloting her program is PUBH 520 (Advanced Topics in Community Health), which contains only graduate students. Her control group consists of undergraduate students taking PUBH 410 (Community Health Education). At the end of the semester and based on her longitudinal data, she finds that, as hypothesized, the PUBH 520 students’ test scores are much higher than the PUBH 410 students’ scores and believes this is due to her learning method. However, you tell her that her study suffers from a certain threat to internal validity. What is that threat? State and explain how this is a threat in relation to the DV. What could Amy do next time to protect against this threat to internal validity?

4. John conducts a safer sex intervention (IV) at one school, Tuffy High School, in order to increase condom use (DV). The treatment condition receives an intensive 8-session program (2- hour sessions, twice per week, 4 weeks total), and the control condition receives a pamphlet on the importance of safer sex. After he analyzes the longitudinal data, he finds that condom use increased in both groups, and there are no statistically significant differences between the two groups. He then realizes a major error in this study design. What type of threat to internal validity plagues his study? State and explain how this is a threat in relation to the DV. What can John do the next time to protect against this threat to internal validity?

Part II. Read the required reading, Amaro et al. (2017), and answer the following questions in essay style.
( Link in file)

1. Amaro et al. (2017) used a “2-group nonrandomized controlled study” or a quasi-experimental study design which, theoretically, is open to more threats to internal validity. The researchers find that there were greater increases in knowledge, self-efficacy, and shopping behaviors (e.g., healthier purchases based on their receipts) among those women who were in the Ser Consciente (2-video) group versus the El Carrito Saludable (1-video) group. The researchers conclude that the 2-video series “shows promise.” What threat to internal validity may have caused changes in these outcomes? State one threat, and explain how this is a threat in relation to each of the three DVs. Pick a different threat to internal validity than those discussed in Part I.

2. How can the study design used in Amaro et al. (2017) be strengthened to minimize overall threats to internal validity and increase confidence in the causal relationship? Explain, and be specific. 2. How can the study design used in Amaro et al. (2017) be strengthened to minimize overall threats to internal validity and increase confidence in the causal relationship? Explain, and be specific.

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