# Survival time analysis, median follow-up time, X-year survival rate

The median follow-up time and the X in X-year survival rate are often far apart in various papers. Is this correct? My personal opinion is that it is good if the Kaplan-Meier survival curve is described and the number of patients is not reduced too much, but I don't know the criteria. I would appreciate it if you could give me some evidence for this.

I appreciate any help you can provide.

Provided that censoring isn't informative, there are data beyond year $$X$$ for $$X$$-year survival, and there are enough events, what you describe isn't necessarily a problem. Here's how to gauge how much of a problem it could be.
$$\widehat{Var}\{\hat{S}(t)\} = \hat{S^2}(t) \sum_{j|t_j \le t} \dfrac{d_j}{n_j (n_j - d_j)}$$
where $$\hat S(t)$$ is the estimated survival through time $$t$$ and $$j$$ is the index of event times, with $$n_j$$ and $$d_j$$ the number of individuals at risk and having events at time $$t_j$$, respectively. Use this variance (or its square root, the standard error) as an estimate of the reliability of the Kaplan-Meier estimator to see the effects of reducing the numbers of individuals at risk and having events at late times.