Sample size determination for estimation of the accuracy of two conditionally independent tests in the absence of a gold standard

• Published in: Preventive veterinary medicine 2005-09, Vol.71 (1), p.1-10
• Main Authors: Georgiadis, Marios P., Johnson, Wesley O., Gardner, Ian A.
• Format: Article
• Language: English
• Subjects: accuracy; animal diseases; Animals; Antibodies, Bacterial - analysis; Cattle; computer software; data analysis; Denmark - epidemiology; disease diagnosis; disease prevalence; Enzyme-Linked Immunosorbent Assay - veterinary; estimation; Hui and Walter model; livestock; Microsoft Excel; Milk - immunology; Models, Statistical; Mycobacterium avium - immunology; Mycobacterium avium - isolation & purification; Paratuberculosis - epidemiology; Paratuberculosis - etiology; Prevalence; Sample Size; sampling; Sensitivity; Sensitivity and Specificity; Specificity; spreadsheets; test sensitivity; test specificity
• ISSN: 0167-5877; 1873-1716
• DOI: 10.1016/j.prevetmed.2005.04.004

We developed an Excel spreadsheet template (available at http://www.epi.ucdavis.edu/diagnostictests/) to calculate sample sizes to estimate sensitivity and specificity with desired precision in the absence of a gold standard. Calculations are predicated on the use of two conditionally independent tests for screening animals from two populations and are based on the methods of Hui and Walter (1980). Sample size calculations rely on asymptotic normality of maximum likelihood (ML) estimates of parameters. Spreadsheets for calculating standard errors for the parameter estimates and for providing ML estimates using cross-tabulated data also are included. An example of application of the methods to bovine paratuberculosis is presented.