Fig. 2
From: Sampling strategies to evaluate the prognostic value of a new biomarker on a time-to-event end-point
Probability Proportional to size (PPS) and Case-Control (CC) sampling from phase I cohort are shown in the upper part (a), left and right, respectively. Dots represents individuals in the strata (case or control and strata = 1 or strata = 2). Arrows correspond to the sampling from phase I to phase II. The number of sampled individuals in each stratum (phase II) depends on the sampling design. Nested Case-Control (NCC) and Counter-matching (CM) sampling are shown below in the figure (b). The lines represent the follow-up over which individuals are observed and the solid lines represented the sampled subjects. Black dot symbol represents the occurrence of an event and the arrow indicated the corresponding sampled control. For NCC, sampling is conducted in the same stratum and for CM, cases are matched with controls from the opposite stratum