Quantitative process measures in interventions to improve employees’ mental health: A systematic literature review and the IPEF framework

Interventions to improve mental health can target individuals, working groups, their leaders, or organisations, also known as the Individual, Group, Leader, and Organisational (IGLO) levels of intervention. Evaluating such interventions in organisational settings is complex and requires sophisticated evaluation designs taking into account the intervention process. In the present systematic literature review, we present state of the-art of quantitative measures of process evaluation. We identified 39 papers. We found that measures had been developed to explore the organisational context, the intervention design, and the mental models of the intervention and its activities. Quantitative process measures are often poorly validated, and only around half of the studies linked the process to intervention outcomes. Fifteen studies used mixed methods for process evaluation. Most often, a qualitative process evaluation was used to understand unexpected intervention outcomes. Despite the existence of theoretical process evaluation frameworks, these were not often employed, and even when included, frameworks were rarely acknowledged, and only selected elements were included. Based on our synthesis, we propose a new framework for evaluating interventions, the Integrative Process Evaluation Framework (IPEF), together with reflections on how we may optimise the use of quantitative process evaluation in conjunction with a qualitative process evaluation.