Which design to evaluate complex interventions? Toward a methodological framework through a systematic review

BACKGROUND: Evaluation of complex interventions (CI) is challenging for health researchers and requires innovative approaches. The objective of this work is to present the main methods used to evaluate CI. METHODS: A systematic review of the scientific literature was conducted to identify methods used for the evaluation of CI. We searched MEDLINE via PubMed databases for articles including an evaluation or a pilot study of a complex intervention, published in a ten-year period. Key-words of this research were (“complex intervention*” AND “evaluation”). RESULTS: Among 445 identified articles, 100 research results or protocols were included. Among them, 5 presented 2 different types of design in the same publication, thus our work included 105 designs. Individual randomized controlled trials (IRCT) represented 21.9% (n = 23) of evaluation designs, randomized clinical trials adaptations 44.8% (n = 47), quasi -experimental designs and cohort study 19.0% (n = 20), realist evaluation 6.7% (n = 7) and other cases studies and other approaches 8.6% (n = 9). A process/mechanisms analysis was included in 80% (n = 84) of these designs. CONCLUSION: A range of methods can be used successively or combined at various steps of the evaluation approach. A framework is proposed to situate each of the designs with respect to evaluation questions. The growing interest of researchers in alternative methods and the development of their use must be accompanied by conceptual and methodological research in order to more clearly define their principles of use.