Correction: Sampling strategies to evaluate the prognostic value of a new biomarker on a time-to-event end-point

Correction: BMC Med Res Methodol 21, 93 (2021)

https://doi.org/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 π_i = P($\xi_i$  = 1|X_i,Δ_i,Z_i) 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 π _i = P( $\xi_i$  = 1|X _i ,Δ _i ), with Δ _i = I(T _i < C _i ), 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 sub-section of the Methods (in the PDF version this is at page 3, first column, paragraph (iv)).

The published version of equation is:

$${\pi}_i=\frac{n/2}{\sum_{i=1}^N{\varDelta}_{\mathrm{i}}}$$

The correct version is given below:

$${\pi}_i=\frac{\sum_{i=1}^N{\varDelta}_i{\xi}_{{i}}}{\sum_{i=1}^N{\varDelta}_{{i}}}$$

The original article has been updated.