摘要：One of the most common challenges in biomedical and psy.hosocial research is missing data, which occurs when respondents refuse to provide answers to sensitive questions and when study.subjects are lost to follow-up during the repeated assessments of longitudinal trials. This paper is the first in a 3-part series focusing on this important topic; it describes different ty.es of missing data and their differential effects on model estimates, focusing on study.design strategies that can be used to prevent or minimize missing data and, thus, maintain the scientific integrity.of the research. The second paper in the series will discuss implementation strategies