Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Critical Care cung cấp cho các bạn kiến thức về ngành y đề tài: Statistics review 11: Assessing risk. | Available online http content 8 4 287 Review Statistics review 11 Assessing risk Viv Bewick1 Liz Cheek1 and Jonathan Ball2 Senior Lecturer School of Computing Mathematical and Information Sciences University of Brighton Brighton UK 2Senior Registrar in ICU Liverpool Hospital Sydney Australia Corresponding author Viv Bewick Published online 30 June 2004 This article is online at http content 8 4 287 2004 BioMed Central Ltd Critical Care 2004 8 287-291 DOI cc2908 Abstract Relative risk and odds ratio were introduced in earlier reviews see Statistics reviews 3 6 and 8 . This review describes the calculation and interpretation of their confidence intervals. The different circumstances in which the use of either the relative risk or odds ratio is appropriate and their relative merits are discussed. A method of measuring the impact of exposure to a risk factor is introduced. Measures of the success of a treatment using data from clinical trials are also considered. Keywords absolute risk reduction attributable risk case-control study clinical trial cross-sectional study cohort study incidence number needed to harm number needed to treat odds ratio prevalence rate ratio relative risk risk ratio Introduction As an example we shall refer to the findings of a prospective cohort study conducted by Quasney and coworkers 1 of 402 adults admitted to the Memphis Methodist Healthcare System with community-acquired pneumonia. That study investigated the association between surfactant protein B and acute respiratory distress syndrome ARDS . Patients were classified according to their thymine cytosine C T gene coding and patients with the C allele present genotype CC or CT were compared with those with genotype TT. The results are shown in Table 1. The risk that an individual with the C allele present will develop ARDS is the probability of such an individual developing ARDS. In the study we can estimate this risk by calculating
