Types of Epidemiological Study Designs III. Based on timing : 1. One-time (one-spot) studies •Conducted at a point in time •An individual is observed at once 2. Longitudinal (Follow-up) studies •Conducted over a period of time •Individuals are followed over a period of time. Types of Epidemiological Study Designs IV. Based on direction of follow-up/data collection: 1. Prospective View Lecture 4 Overview of study designs STUDENT.pdf from PHP 2120 at Brown University. Overview of Study Designs in Epidemiological Studies Lecture 4: September 21, 2021 Lecture 4 Sept 18, Issues of study design have been addressed in terms of combining randomized trials and observational studies in evaluating preventive interventions such as Bacillus Calmette-Guérin vaccination (Colditz et al., 1994) and mammography screening (Desmissie et al., 1998). When one is interpreting the apparent heterogeneity in the results, it is important to step back and ask what is the relationship being evaluated under these different study designs? For example, a randomized Overview of study designs 85 Outline of an intervention trial. Study population Direction of inquiry Intervention group Outcome No outcome Outcome No outcome Control group allocation implemented by the investigator Example 5.1.The Women's Intervention Nutrition Study was set up to assess whether a low-fat diet will reduce cancer recurrence and improve sur- "the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems". Various methods can be used to carry out epidemiological investigations: surveillance and descriptive studies can be used to study distribution;