Quality assessment of meta-analyses.

aNo search for grey literature described. bData combined appropriately using random-effects models, but studies grouped according to received dose (treatment dose * adherence). The advisability and validity of this approach is uncertain. cData combined appropriately using random-effects models, but data for hip fracture was used for 4/16 trials when the primary endpoint assessed was total fracture. dData combined appropriately using Cox proportional-hazards models, but method of assessment of vitamin D intake differed between treatment and control groups. ePartly funded by a manufacturer of vitamin D supplements. Quality assessment of meta-analyses.