You developed a new drug that you believe is effective in reducing appetite. As a result of some preliminary research, you have been given a small grant to design an experiment that tests the effectiveness of this new drug on morbidly obese individuals.
Clearly describe the potential threats to both the internal and external validity of this study. What are ways to work around this in the future?
Internal validity is an evaluation of whether any differences between your groups are truly due to your treatment. In this case, that means that internal validity indicates how likely it is that any reduction in appetite is due to the drug, and not some other factor. If you get creative, you can think of several threats to internal validity (i.e., several other factors that might lead to decreases in appetite). For example, maybe having people track what they eat decreases their appetite, or maybe having to report how hungry they are makes them less likely to say they're really hungry. Both of these factors could make it appear that your drug decreases ...
The solution discusses the independent group designs case study.