What are the three major problems caused by attrition in a study?

The selection of the second set of issues as the correct answer captures the critical implications of attrition in research studies. Attrition refers to the loss of participants over the duration of a study, which can significantly affect the integrity and interpretation of the research findings.

The mention of unbalanced group characteristics highlights how attrition can lead to differences between groups that were not intended by the study design. If certain participants drop out, it can skew the demographics and baseline characteristics of the groups, creating a situation where they are no longer comparable.

Lower statistical power is a consequence of reduced sample sizes due to attrition. When participants drop out of a study, the remaining sample may not be large enough to detect significant effects or differences, which can impede the study's ability to produce reliable outcomes.

The issue of reduced representativeness is also crucial. If the participants who drop out differ systematically from those who remain in the study, the findings may not be generalizable to the broader population. This compromises the external validity of the research, as the remaining sample may not adequately reflect the characteristics of the intended population.

Collectively, these problems underscore why addressing attrition is vital for maintaining the robustness and validity of research outcomes.