Sandra Eldridge|Deborah Ashby|Catherine Bennett|Melanie Wakelin|Gene Feder
Internal and external validity of cluster randomised trials: systematic review of recent trials
assess aspects internal validity recently published cluster randomised trials explore reporting information useful assessing external validity trialsreview 34 cluster randomised trials primary care published 2004 2005 seven journals british medical journal british journal general practice family practice preventive medicine annals internal medicine journal general internal medicine pediatricsnational library medicine medline via pubmedto assess aspects internal validity extracted data appropriateness sample size calculations analyses methods identifying recruiting individual participants blinding explore reporting information useful assessing external validity extracted data cluster eligibility cluster inclusion retention cluster generalisability feasibility acceptability intervention health providers clusters21 62 trials accounted clustering sample size calculations 30 88 analysis quarter potentially biased procedures surrounding recruitment identification patients individual participants blind allocation status 19 56 outcome assessors blind 15 44 almost half reports information relating generalisability clusters poorly reported two fifths information feasibility acceptability interventioncluster randomised trials essential evaluating certain types interventions issues affecting internal validity appropriate sample size calculations analysis widely disseminated better addressed researchers blinding identifying recruiting patients allocation status recommended always carried may fewer barriers internal validity trials individual participants recruited external validity seems poorly addressed many trials yet arguably important internal validity judging quality basis healthcare intervention