TABLE 5-5 Types of Experimental and Quasi-Experimental Evidence and Examples of Their Uses

Type of Evidence

Questions That Could Be Addressed

Specific Applications

Randomized Controlled Trial (RCT)

Compared with another intervention, are the obesity outcomes better for individuals assigned at random to receive this intervention than for those assigned not to receive the intervention? (“What” question)

A randomized controlled trial of a manipulated nutrition program in two groups of obese adults who were placed in the program based on a coin flip (The random assignment usually balances individual characteristics across those who receive or do not receive the program so that the result can be interpreted as “all other things being equal”; some statistical controls may be required.)

Quasi-experimental Study

Compared with another intervention, are the obesity outcomes better with this intervention when administered to adults in two similar communities? (“What” question)

A matched-cohort study design comparing obesity outcomes of a manipulated nutrition program in two communities (The two communities are the groups that are matched on relevant characteristics; other potential influences on intervention outcomes are statistically controlled.)


Using ongoing obesity measures as control data in a group of children, is body mass reduced when this intervention is administered in alternating cycles? (“What” question)

An interrupted time series study tracking changes in obesity outcomes over time when a nutrition program is administered periodically

quasi-experimental approaches in other fields that are recommended for increased emphasis in research on obesity prevention.

Qualitative Research

Qualitative research evidence is typically derived from documentary sources, field observations, interviews, and open-ended verbal interactions between participants and researchers. Examples of studies that fall within this category include logic modeling or program theory analysis, ethnographic studies, focus group or key informant interviews, content or documentary analysis, case studies, some intervention process delivery and implementation monitoring, and evaluability assessments of programs and interventions. Qualitative research approaches give researchers the ability to assess perceptions of respondents at a much richer level than is possible using questionnaires with fixed responses.

Qualitative methods employ emergent designs (not preset, as in quantitative methods) and contextualized understandings of phenomena. Those investigating an intervention will want in-depth information on how people interact with the intervention and with different variables in that context. Questions and data-gathering techniques may be expanded or modified as data are collected. This type of research may

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