I am designing a cohort study whose main objective is estimation of the survival probability for the group.

Many packages are available to estimate the sample size for a single mean or a single proportion based on the margin of error (or CI width), yet, to my knowledge there is none on single-arm time-to-event outcomes. Any guidance?

The calculator: Sample size calculation for one sample non-parametric survival (survival proportion) | Kengo Nagashima - Keio University

I would appreciate if you could explain how to calculate ‘Null survival probability’ and ‘Alternative survival probability’

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Thank you for the link, but this seems to still do a “one sample test” comparing a sample’s survival probability to a fixed probability (null hypothesis testing), which is different from what I am looking for (precision).