title: GRADE guidelines 6. Rating the quality of evidence--imprecision.
abstract: GRADE suggests that examination of 95% confidence intervals (CIs) provides the optimal primary approach to decisions regarding imprecision. For practice guidelines, rating down the quality of evidence (i.e., confidence in estimates of effect) is required if clinical action would differ if the upper versus the lower boundary of the CI represented the truth. An exception to this rule occurs when an effect is large, and consideration of CIs alone suggests a robust effect, but the total sample size is not large and the number of events is small. Under these circumstances, one should consider rating down for imprecision. To inform this decision, one can calculate the number of patients required for an adequately powered individual trial (termed the "optimal information size" [OIS]). For continuous variables, we suggest a similar process, initially considering the upper and lower limits of the CI, and subsequently calculating an OIS. Systematic reviews require a somewhat different approach. If the 95% CI excludes a relative risk (RR) of 1.0, and the total number of events or patients exceeds the OIS criterion, precision is adequate. If the 95% CI includes appreciable benefit or harm (we suggest an RR of under 0.75 or over 1.25 as a rough guide) rating down for imprecision may be appropriate even if OIS criteria are met.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario L8N 3Z5, Canada. guyatt@mcmaster.ca
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Oxman
authors.forename: Regina
authors.initials: R
authors.lastname: Kunz
authors.forename: Jan
authors.initials: J
authors.lastname: Brozek
authors.forename: Pablo
authors.initials: P
authors.lastname: Alonso-Coello
authors.forename: David
authors.initials: D
authors.lastname: Rind
authors.forename: P J
authors.initials: PJ
authors.lastname: Devereaux
authors.forename: Victor M
authors.initials: VM
authors.lastname: Montori
authors.forename: Bo
authors.initials: B
authors.lastname: Freyschuss
authors.forename: Gunn
authors.initials: G
authors.lastname: Vist
authors.forename: Roman
authors.initials: R
authors.lastname: Jaeschke
authors.forename: John W
authors.initials: JW
authors.lastname: Williams
authors.forename: Mohammad Hassan
authors.initials: MH
authors.lastname: Murad
authors.forename: David
authors.initials: D
authors.lastname: Sinclair
authors.forename: Yngve
authors.initials: Y
authors.lastname: Falck-Ytter
authors.forename: Joerg
authors.initials: J
authors.lastname: Meerpohl
authors.forename: Craig
authors.initials: C
authors.lastname: Whittington
authors.forename: Kristian
authors.initials: K
authors.lastname: Thorlund
authors.forename: Jeff
authors.initials: J
authors.lastname: Andrews
authors.forename: Holger J
authors.initials: HJ
authors.lastname: Schünemann
mesh_terms: D016001:Confidence Intervals; D019317:Evidence-Based Medicine / Q000592:standards*; D006801:Humans; D015201:Meta-Analysis as Topic; D017410:Practice Guidelines as Topic; D016032:Randomized Controlled Trials as Topic / Q000592:standards*; D012306:Risk; D018401:Sample Size