Nested and multipart prospective observational studies, flaming fiasco or efficiently economical?: The Brain, Bone, Heart case study.

Background: Collecting new data from cross-sectional/survey and cohort observational study designs can be expensive and time-consuming. Nested (hierarchically cocooned within an existing parent study) and/or Multipart (≥ 2 integrally interlinked projects) study designs can expand the scope of a prospective observational research program beyond what might otherwise be possible with available funding and personnel. The Brain, Bone, Heart (BBH) study provides an exemplary case to describe the real-world advantages, challenges, considerations, and insights from these complex designs. MAIN: BBH is a Nested, Multipart study conducted by the Specialized Center for Research Excellence (SCORE) on Sex Differences at Emory University. BBH is designed to examine whether estrogen insufficiency-induced inflammation compounds HIV-induced inflammation, leading to end-organ damage and aging-related co-morbidities affecting the neuro-hypothalamic-pituitary-adrenal axis (brain), musculoskeletal (bone), and cardiovascular (heart) organ systems. Using BBH as a real-world case study, we describe the advantages and challenges of Nested and Multipart prospective cohort study design in practice. While excessive dependence on its parent study can pose challenges in a Nested study, there are significant advantages to the study design as well. These include the ability to leverage a parent study's resources and personnel; more comprehensive data collection and data sharing options; a broadened community of researchers for collaboration; dedicated longitudinal research participants; and, access to historical data. Multipart, interlinked studies that share a common cohort of participants and pool of resources have the advantage of dedicated key personnel and the challenge of increased organizational complexity. Important considerations for each study design include the stability and administration of the parent study (Nested) and the cohesiveness of linkage elements and staff organizational capacity (Multipart).

Conclusion: Using the experience of BBH as an example, Nested and/or Multipart study designs have both distinct advantages and potential vulnerabilities that warrant consideration and require strong biostatistics and data management leadership to optimize programmatic success and impact.