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  "body": "\n## Summary\n\nThe Nelson–Aalen estimator is a nonparametric estimator of the cumulative [[hazard function|Y959NKQ3XW]] from right-[[censored|MY8ZZP84NP]] data.\nAt each observed event time it adds the number of events divided by the number of subjects at risk.\nIt is the natural estimator in the counting process approach to survival analysis, where its large-sample theory follows from martingale results.\nTaking $e^{-\\hat H(t)}$ gives an estimator of the survival function close to the [[Kaplan–Meier estimator|B7AJ8RWZRC]].\n\n## Explanations\n\n### L1 human\n\nThe cumulative hazard adds up the risk of the event over time.\nAt each moment when someone has the event, the Nelson–Aalen estimator adds \"events now divided by people still at risk\".\nIf one person of four dies, it adds $1/4$; if later one person of two dies, it adds $1/2$.\nThe total grows faster when events are frequent among those still at risk.\nPlotting it shows whether the hazard is constant (a straight line) or changes with time.\n",
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