Correction: Sampling strategies to evaluate the prognostic value of a new biomarker on a time-to-event end-point (BMC Medical Research Methodology, (2021), 21, 1, (93), 10.1186/s12874-021-01283-0)

Following publication of the original article [1], the authors noticed the two errors. The first one in the Notation setting sub-section of the Methods (in the PDF version this is at page 2, second column, lines 9-11). The published version of the phrase is: Let (Formula presented.) being the inclusion probability of subject i for the phase II sample, conditional on being selected at phase I. The correct version is given below: Let (Formula presented.), with Δi = I(Ti < Ci), being the inclusion probability of subject i for the phase II sample, conditional on being selected at phase I. A second error was found in the Phase II sample subsection of the Methods (in the PDF version this is at page 3, first column, paragraph (iv)). The published version of equation is: (Formula presented.).