D. Campbell, Factors relevant to the validity of experiments in social settings., Psychological Bulletin, vol.54, issue.4, pp.297-312, 1957.
DOI : 10.1037/h0040950

S. Green and J. Higgins, Glossary. Cochrane handbook for systematic reviews of interventions 4.2.5. Available, 2005.

L. Fisher, D. Dixon, J. Herson, R. Frankowski, and M. Hearon, Intention to treat in clinical trials, Statistical issues in drug research and development, pp.331-350, 1990.

S. Hollis and F. Campbell, What is meant by intention to treat analysis? Survey of published randomised controlled trials, BMJ, vol.319, issue.7211, pp.670-674, 1999.
DOI : 10.1136/bmj.319.7211.670

J. Lachin, Statistical Considerations in the Intent-to-Treat Principle, Controlled Clinical Trials, vol.21, issue.3, pp.167-189, 2000.
DOI : 10.1016/S0197-2456(00)00046-5

A. Donner and N. Klar, Design and analysis of cluster randomization trials, 2000.

D. Murray, Design and analysis of grouprandomized trials, 1998.

S. Puffer, D. Torgerson, and J. Watson, Evidence for risk of bias in cluster randomised trials: review of recent trials published in three general medical journals, BMJ, vol.327, issue.7418, pp.785-789, 2003.
DOI : 10.1136/bmj.327.7418.785

O. Ukoumunne, M. Gulliford, S. Chinn, J. Sterne, and P. Burney, Methods for evaluating area-wide and organisation-based interventions in health and health care: A systematic review, Health Technol Assess, vol.3, p.92, 1999.

J. Bland, Cluster randomised trials in the medical literature: two bibliometric surveys, BMC Medical Research Methodology, vol.328, issue.1, p.21, 2004.
DOI : 10.1136/bmj.328.7441.702

M. Campbell, D. Elbourne, and D. Altman, CONSORT statement: extension to cluster randomised trials, BMJ, vol.328, issue.7441, pp.702-708, 2004.
DOI : 10.1136/bmj.328.7441.702

URL : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC381234

S. Edwards, D. Braunholtz, R. Lilford, and A. Stevens, Ethical issues in the design and conduct of cluster randomised controlled trials, BMJ, vol.318, issue.7195, pp.1407-1409, 1999.
DOI : 10.1136/bmj.318.7195.1407

D. Elbourne and M. Campbell, Extending the CONSORT statement to cluster randomized trials: for discussion, Statistics in Medicine, vol.319, issue.3, pp.489-496, 2001.
DOI : 10.1002/1097-0258(20010215)20:3<489::AID-SIM806>3.0.CO;2-S

M. Campbell, Cluster randomized trials in general (family) practice research, Statistical Methods in Medical Research, vol.9, issue.2, pp.81-94, 2000.
DOI : 10.1191/096228000676246354

A. Farrin, I. Russell, D. Torgerson, and M. Underwood, Differential recruitment in a cluster randomized trial in primary care: the experience of the UK Back pain, Exercise, Active management and Manipulation (UK BEAM) feasibility study, Clinical Trials, vol.2, issue.2, pp.119-124, 2005.
DOI : 10.1191/1740774505cn073oa

S. Eldridge, D. Ashby, C. Bennett, M. Wakelin, and G. Feder, Internal and external validity of cluster randomised trials: systematic review of recent trials, BMJ, vol.336, issue.7649, pp.876-880, 2008.
DOI : 10.1136/bmj.39517.495764.25

M. Taljaard, A. Donner, and N. Klar, Imputation Strategies for Missing Continuous Outcomes in Cluster Randomized Trials, Biometrical Journal, vol.71, issue.3, pp.329-345, 2008.
DOI : 10.1002/bimj.200710423

S. Hunsberger, D. Murray, C. Davis, and R. Fabsitz, Imputation strategies for missing data in a school-based multi-centre study: the Pathways study, Statistics in Medicine, vol.5, issue.2, pp.305-316, 2001.
DOI : 10.1002/1097-0258(20010130)20:2<305::AID-SIM645>3.0.CO;2-M

D. Torgerson and C. Torgerson, Designing randomised trials in health, education and the social sciences. An introduction, 2008.

S. Hahn, S. Puffer, D. Torgerson, and J. Watson, Methodological bias in cluster randomised trials, BMC Medical Research Methodology, vol.4, issue.suppl 3, p.10, 2005.
DOI : 10.1186/1471-2288-4-21

M. Jordhoy, P. Fayers, M. Ahlner-elmqvist, and S. Kaasa, Lack of concealment may lead to selection bias in cluster randomized trials of palliative care, Palliative Medicine, vol.49, issue.1, pp.43-49, 2002.
DOI : 10.1191/0269216302pm523oa

R. Kessler, R. Little, and R. Groves, Advances in Strategies for Minimizing and Adjusting for Survey Nonresponse, Epidemiologic Reviews, vol.17, issue.1, pp.192-204, 1995.
DOI : 10.1093/oxfordjournals.epirev.a036176

P. Rosenbaum and D. Rubin, The central role of the propensity score in observational studies for causal effects, Biometrika, vol.70, issue.1, pp.41-55, 1983.
DOI : 10.1093/biomet/70.1.41

P. Rosenbaum and D. Rubin, Reducing Bias in Observational Studies Using Subclassification on the Propensity Score, Journal of the American Statistical Association, vol.6, issue.387, pp.516-524, 1984.
DOI : 10.1080/01621459.1984.10478078

P. Ravaud, R. Flipo, I. Boutron, C. Roy, and B. Giraudeau, ARTIST (osteoarthritis intervention standardized) study of standardised consultation versus usual care for patients with osteoarthritis of the knee in primary care in France: Pragmatic randomised controlled trial Primary care management of major depression in patients aged, BMJ, vol.338, p.55, 2008.

J. Nicholas, M. Gulliford, R. Campbell, F. Starkey, J. Holliday et al., Commentary. What is a propensity score? Br J Gen Pract 58: 687. 29 An informal school-based peer-led intervention for smoking prevention in adolescence (ASSIST): A cluster randomised trial, Lancet, vol.371, pp.1595-1602, 2008.

S. Bellary, O. Hare, J. Raymond, N. Gumber, A. Mughal et al., Enhanced diabetes care to patients of south Asian ethnic origin (the United Kingdom Asian Diabetes Study): a cluster randomised controlled trial, The Lancet, vol.371, issue.9626, pp.1769-1776, 2008.
DOI : 10.1016/S0140-6736(08)60764-3