spec: add survival-kaplan-meier specification

[github-actions]

New Specification: survival-kaplan-meier

Related to #2441

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specification.md

survival-kaplan-meier: Kaplan-Meier Survival Plot

Description

A Kaplan-Meier survival plot visualizes the probability of survival (or event-free time) over a time period using a step function. It is the standard method for estimating survival functions from time-to-event data, handling censored observations where the event has not yet occurred. The plot shows how survival probability decreases over time, with optional confidence intervals and comparison between groups.

Applications

• Medical research tracking patient survival rates after diagnosis or treatment
• Reliability engineering analyzing time-to-failure for equipment or components
• Customer analytics measuring time-to-churn or subscription retention
• Clinical trials comparing survival outcomes between treatment and control groups

Data

• time (numeric) - Time to event or censoring (e.g., days, months, years)
• event (binary) - Event indicator (1 = event occurred, 0 = censored)
• group (categorical, optional) - Grouping variable for comparing survival curves
• Size: 50-1000 observations
• Example: Clinical trial data with patient survival times and treatment groups

Notes

• Use step function (not smooth curves) to accurately represent discrete event times
• Include 95% confidence intervals as shaded bands around the survival curve
• Mark censored observations with tick marks on the curve
• When comparing groups, use distinct colors and include a legend
• Consider adding median survival time annotation and at-risk table below the plot
• Log-rank test p-value can be included when comparing groups

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