Data analysis

O15.1 THE APPLICATION OF STATISTICAL TESTS TO CLINICAL DIAGNOSTICS

M. Boggess¹, M. Guest², J. Attia², C. D’Este², A. Brown³.¹Stata Corporation, College Station, TX, USA; ²Faculty of Health, University of Newcastle, Callaghan, NSW, Australia; ³Population Health, Macquarie Area Health Service, Dubbo, NSW, Australia

Introduction: Medical diagnostic tests are developed by clinicians to obtain reliable diagnoses. Thus not all diagnostic tests give results that are amenable to statistical examination. This poses a particular problem for epidemiologists: in order to be able find significant evidence of an effect of exposure we need to use a sample size appropriate for the statistical test being used. This may require examining the test results of many subjects.

Methods: A good example of an intractable diagnostic test is the L’Anthony Desaturated Panel-D-15 for colour vision deficiency. An opthalmologist makes a diagnosis, into one of several categories, by examining a diagram that is a representation of the results of the test. In the 1980s two attempts (Bowman and Vingrys et al) were made to compute a numerical index from the L’Anthony test results. While this made it possible to test hypotheses concerning exposure, the indices are difficult to interpret and it has been unclear as to the distributional properties of these indices. We examine the calculation of these indexes in the light of statistical data reduction techniques.

Results: We show that Vingrys’ “moment of inertia” method is essentially principle component analysis, a data reduction method which uses matrix methods, commonly used in social sciences. Using data from the Australian Aircraft Maintenance Technician study, we apply discriminant analysis to derive a decision rule for diagnosis, which we compare to current methods using ROC curves.

O15.2 INVESTIGATING COLOUR VISION IMPAIRMENT IN AIRCRAFT MAINTENANCE TECHNICIANS

M. Guest¹, J. Attia¹, C. D’Este¹, A. Brown², M. Boggess³. …