Problematiche metodologiche nella pianificazione e nel calcolo della dimensione del campione di un cluster randomized trial (CRT): il caso del Progetto Raffaello

Cluster randomization, where groups (or clusters) of subjects, rather than single individuals, are randomly allocated to intervention groups, is increasingly being adopted in studies to evaluate interventions directed at a whole area or healthcare unit (such as a hospital ward, or a medical practice). Studies that use this method of randomization are referred to as cluster randomized trials (CRT) and have considerable organizational and economic advantages. However, CRTs have distinctive ethical issues that need to be considered and most importantly, require a series of methodological modifications during data analysis and calculation of sample size (during which additional parameters, such as the intracluster correlation coefficient and the design effect, need to be obtained). Methodological guidelines for conducting CRTs have been published in November 2002. However, no scientific articles dealing with the methodology associated with the design and analysis of this type of study have yet been published in Italian. The aim of this article, therefore, is to provide methodological support to healthcare researchers who are planning a CRT, through a description of the methodology used in the Raffaello project. This project is in the start-off phase in the Marche and Abruzzo regions of Italy and represents an excellent case study, it being a CRT aimed at evaluating the efficacy of a Disease Management model in the general population (with general practitioners therefore, being the cluster of randomization).