A case study of a theory-based method for identifying and reporting core functions and forms of evidence-based interventions

Adaptation of existing evidence-based interventions (EBIs) to improve their fit in new contexts is common. A critical first step in adaptation is to identify core functions (purposes) and forms (activities) of EBIs. Core functions should not be adapted as they are what account for the efficacy of EBIs. Despite their importance, core functions are rarely identified by EBI developers; methods for identifying them post hoc are lacking. We present a case study of theory-based methods for identifying core functions and forms post hoc. We developed these methods as the first step in a larger effort to adapt an existing EBI to improve the timeliness of referrals to hospice to a new patient population and care setting. Our methods were rooted in the Planned Adaptation Model (PAM). Through our case study, we developed six steps for identifying core functions and forms, as well as accompanying tools and methods. Our case study further operationalized PAM in several ways. Where PAM offered guiding tenets for identifying core functions and forms (review existing EBI materials, conduct primary data collection, and identify the theory of change), we produced specific tools (interview guides and codebooks) and methods (sampling approaches and analytic methods). Our case study extended PAM with the addition of two steps in the process of identifying core functions and forms: (a) identifying the usual care pathway, including barriers to the outcome of interest encountered in usual care, and (b) mapping EBI core functions onto an extant theory. Identifying core functions and forms is a critical first step in the adaptation process to ensure adaptations do not inadvertently compromise the efficacy or effectiveness of the EBI by compromising core functions. Our case study presents step-by-step methods that could be used by researchers or practitioners to identify core functions and forms post hoc.