In Exercises 21–28, determine whether the study is an experiment or an observational study, and then identify a major problem with the study.
Sleep Study When designing the study of a new treatment for insomnia in adults, researchers were criticized because their test subjects consisted of 75 college students. They then expanded the study so that 750 college students were given the treatment.

Verified step by step guidance

1. Identify the type of study: Determine if the study is an experiment or an observational study. An experiment involves the manipulation of variables to observe effects, while an observational study involves observing subjects without intervention.
2. Assess the study design: In this case, the study involves giving a treatment to a group of subjects, which indicates that it is an experiment since the researchers are actively applying a treatment to observe its effects.
3. Evaluate the sample selection: Consider the characteristics of the sample used in the study. Here, the sample consists entirely of college students, which may not be representative of the general adult population with insomnia.
4. Identify potential biases: Recognize that using only college students can introduce selection bias, as this group may not accurately reflect the diversity of the adult population in terms of age, lifestyle, and other factors that could affect insomnia.
5. Suggest improvements: Propose ways to address the identified problem, such as expanding the sample to include a more diverse range of adults from different age groups and backgrounds to improve the generalizability of the study results.

Key Concepts

Experimental vs. Observational Study

An experimental study involves the manipulation of variables to determine cause-and-effect relationships, while an observational study observes subjects without intervention. In the sleep study, the researchers applied a treatment to the subjects, indicating it is an experimental study.

Sample Size and Generalizability

Sample size refers to the number of participants in a study, which can affect the reliability of the results. The concern in this study arises from the fact that the sample consisted solely of college students, which may limit the generalizability of the findings to the broader population of adults suffering from insomnia.

Selection Bias

Selection bias occurs when the participants included in a study are not representative of the larger population, potentially skewing results. In this case, using only college students may introduce selection bias, as their sleep patterns and responses to treatment may differ significantly from those of older adults or individuals with varying lifestyles.