title: [Sample size and number needed to treat--a statistical case study].
abstract: The sample size necessary in each group to detect a significant effect of a vaccine on a given disease in a randomised clinical trial (RCT) can be calculated from the observed disease incidence without vaccine, the expected incidence with vaccine, and the desired level of significance and statistical power of the study. In this example, sample size is calculated for an RCT of the effect of pneumococcal vaccine on the incidence of pneumococcal sepsis. The number of persons needed to be vaccinated to prevent one episode of pneumococcal sepsis can be similarly calculated from the observed incidences with and without vaccine.
authors.affiliation: Epidemiafdeling M, H:S Rigshospitalet. kirsten.moller@dadlnet.dk
authors.forename: K
authors.initials: K
authors.lastname: Møller
authors.forename: G
authors.initials: G
authors.lastname: Kronborg
authors.forename: A
authors.initials: A
authors.lastname: Dirksen
mesh_terms: D006801:Humans; D015994:Incidence; D015233:Models, Statistical; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage* / Q000592:standards / Q000600:supply & distribution; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data*; D018401:Sample Size; D018805:Sepsis / Q000453:epidemiology / Q000382:microbiology / Q000517:prevention & control
chemical_list: D022242:Pneumococcal Vaccines