Cluster randomized trials of cancer screening interventions: are appropriate statistical methods being used?

The design and analysis of cluster randomized trials can require more sophistication than individually randomized trials. However, the need for statistical methods that account for the clustered design has not always been appreciated, and past reviews have found widespread deficiencies in methodology and reporting. We reviewed cluster randomized trials of cancer screening interventions published in 1995-2010 to determine whether the use of appropriate statistical methods had increased over time. Literature searches yielded 50 articles reporting outcome analyses of cluster randomized trials of breast, cervix and colorectal cancer screening interventions. Of studies published in 1995-1999, 2000-2002, 2003-2006 and 2007-2010, 55% (6/11), 82% (9/11), 92% (12/13) and 60% (9/15) used appropriate analytic methods, respectively. Results were suggestive of a peak in 2003-2006 (p =.06) followed by a decline in 2007-2010 (p =.08). While the sample of studies was small, these results indicate that many cluster randomized trials of cancer screening interventions have had deficiencies in the application of correct statistical procedures for the outcome analysis, and that increased adoption of appropriate methods in the early and mid-2000's may not have been sustained.