Nelson–Aalen estimator
= Nelson–Aalen estimator
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{title2=$\widehat H(t)$}
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The Nelson–Aalen estimator of the cumulative hazard is $\widehat H(t)=\sum_{t_j\leq t}d_j/r_j$, where $d_j$ events occur among $r_j$ individuals at risk at event time $t_j$.