• Epidemiological methods;
  • Dose—response relationships;
  • Pneumoconiosis;
  • Diagnostic errors


Radiological assessment of pneumoconiosis is an example of a dichotomized variable, namely one that is analysed as a binary response but in fact has an underlying continuum, which in this case is not measurable. Estimates of exposure—response relationships vary greatly for different observers of a dichotomized response variable because of random error of measurement and differences in the threshold implicitly chosen by each observer for categorizing cases. We present a method of using the biserial correlation coefficient and normal distribution theory to estimate exposure—response relationships at any required threshold for each observer. Exposure—response relationships can also be corrected for random observational error using the reliability coefficient, calculated as the tetrachoric correlation between repeat observations by readers.