Logic model development through a feasibility RCT for a group-based weight management programme

Area of Science:

• Clinical psychology
• Obesity interventions
• Health services research

Background:

• Clinical psychology interventions for obesity are often individualized.
• Healthcare interventions rely on logic models detailing mechanisms, outcomes, and contexts.
• PROGROUP is a novel group-based weight management intervention for severe obesity.

Purpose of the Study:

• To assess the empirical validity of the PROGROUP intervention's logic model.
• To test if PROGROUP's components yield intended outcomes and how.
• To determine if PROGROUP can be practically implemented and how delivery affects the program.

Main Methods:

• Realist evaluation of the PROGROUP logic model using a pre-randomized controlled trial (RCT) feasibility study.
• Elicited the logic model and compared it with feasibility data from NHS sites (2021-2023).
• Revised the logic model based on data, assessing tolerance for delivery variations.

Main Results:

• The initial logic model outlined a sequence of mechanisms for weight loss, including group identity reinforcement.
• Necessary contexts included sufficient population, group retention, suitable location, facilitator training, and support.
• Revisions focused on delivery components and contextual assumptions, with scope to simplify referral mechanisms.

Conclusions:

• The logic model requires refinement in delivery and context, not core therapeutic mechanisms.
• Different professional groups can implement the PROGROUP model.
• Realist evaluation of feasibility studies enhances intervention logic models and identifies conditions for wider use.