Accommodating covariates in roc analysis
Despite the considerable numbers of estimation methods, applications of the methodology in clinical studies are still lacking.
The value of time-dependent ROC curve methods has been re-established.
The sensitivity is defined as the probability of a diseased individual being predicted as having the disease (true-positive) and the specificity as the probability of a non-diseased individual being predicted as not having the disease (true-negative).
These probabilities change as the threshold value for the marker changes and the value or range of threshold values chosen depends on the trade-off that is acceptable between failing to detect disease and falsely identifying disease with the test .
This type of discrimination has more clinical relevance than the other definitions (I/D and I/S) and hence C/D definition has commonly been used by clinical applications [ is identified, thus a global accuracy summary is usually desired.ROC (receiver operating characteristic) curve analysis is well established for assessing how well a marker is capable of discriminating between individuals who experience disease onset and individuals who do not.The classical (standard) approach of ROC curve analysis considers event (disease) status and marker value for an individual as fixed over time, however in practice, both the disease status and marker value change over time.Information and signalling of future disease identification may be given by a single continuous measurement marker or a score.
A single measurement could be any clinical measure such as cell percentage in the synthesis phase to detect breast cancer  used the prognostic score of four covariates (age, platelet count, prothrombin time, and serum alpha-fetoprotein level) to predict compensated cirrhosis patients’ survival and also used a score of three baseline characteristics (age, white blood cell and performance status) to predict event-free survival (EFS) in acute leukaemia patients.illustrate the cases and controls that contribute to the three definitions of sensitivity and specificity (C/D and I/D with the baseline marker, and I/S with both the baseline and longitudinal markers), with closed circles indicate individuals who had an event, open circles indicate individuals who had censored event-times.