CALCULATION OF ROC CURVES IN MULTIDIMENSIONAL LIKELIHOOD RATIO BASED SCREENING WITH DOWNS-SYNDROME AS A SPECIAL CASE

Objectives-The development of algorithms and computer programs for the analysis of screening performance in situations with multiple normall y (Gaussian) distributed selection markers and a priori risks dependin g on a stratification of the population. Methods-The S-PLUS programmin g language was used to construct programs producing distributions of l og likelihood ratios based on the Monte Carlo simulation. These distri butions were used to construct programs for the calculation of roc cur ves, including a possible stratification of the population. Results-S- PLUS programs for the analysis of screening performance are listed and described. The programs can be used without any special knowledge of S-PLUS. An example of the use of the programs is given.