hazard function
an estimate of the hazard of death at each event time $$t$$, using available data, and then use these hazards to produce a survival curve by multiplying $$(1-hazard)$$ terms.
How do we estimate hazards? $$$$$$h_i = \frac{# \ events\ at\ t = i}{# \ at\ risk\ at\ t = i} = \frac{Y_i}{n_i}$$