Use cases for using a Human Studies Database were first elicited from our CTSA colleagues. One of those use cases, “Research Characterization—Report research design,” had a high priority, motivating the need for a Study Design Typology. We defined this typology [3
] through an iterative process over 8 months. The design goal was to identify the most parsimonious set of unambiguous factors that will correctly classify any study on individual humans into a set of common study design types.
A series of use cases were created to establish the scope of studies to be characterized. Authoritative methodology sources were consulted [4
]. Reference models of clinical research (e.g., CDISC [7
], BRIDG [8
], OBI [9
]) were consulted but we found little formal modeling of study design types. The typology was presented for feedback to biostatisticians, epidemiologists, and informaticians and at CTSA and other institutions.
The Typology scopes Human Studies as any study collecting or analyzing data about individual humans, whole or in part, living or dead. Studies on populations, organisms, decision strategies, etc. are not considered human studies in our typology. This scope includes all studies that would require human subjects approval and beyond: e.g., autopsy, chart review, expression profiles of surgical pathology, shopping habits, utility assessment, scaled instrument development using data from individual humans, etc.
Human studies are next classified as Qualitative or Quantitative (). Qualitative research techniques seek in-depth understanding through loosely structured mainly verbal data and field observations rather than measurements. Quantitative research studies are systematic investigations of quantitative properties, phenomena, and their relationships, and involve the gathering and analysis of data that are expressed in numerical form.
Qualitative studies were tentatively broken out into Field Studies, Lab-based studies, or Focus Groups. This branch of the typology is under development and was not evaluated in the work we report here.
Quantitative studies are split into Interventional () and Observational () Studies. Interventional studies are ones where the investigator assigns one or more interventions to a study participant. Observational studies are ones where the investigator has no role in what treatment or exposures a study participant receives, but only observes participants for outcomes of interest.
We defined four high-level study design types for interventional studies, based on the number of control groups, whether the participant serves as his/her own control, and whether treatment and control periods are repeated for a single participant. These factors are factual and independent of judgment, and the permissible values are exhaustive and mutually exclusive, facilitating full partitioning of all interventional studies into one of these four study design types.
These high-level study types (in red in the Figures) represent distinct approaches to human investigations that are each subject to distinct sets of biases and interpretive pitfalls. Additional descriptors elaborate on secondary design and analytic features that introduce or mitigate additional validity concerns ().
Additional Descriptors for Interventional Study Designs.Each of the four design types can be further described by some or all of these descriptors.
For the quantitative observational studies subtree, we defined five high-level study design types, based on the number of control groups, whether the main control group was defined by case (outcome) or exposure (predictor) status, whether the case and control are in the same person, and whether outcomes are measured at the same time as predictors or after. Like the discriminatory factors for interventional studies, these factors exhaustively and mutually exclusively partition observational studies into one of these five design types. Additional descriptors also apply to these observational study types (not shown), although some descriptors apply only to some study types.
Mixed method studies are accommodated in this typology by classifying all methods applicable to a study (e.g., interventional with qualitative outcomes assessment).