Lifelines Survival Analysis

WHENWhen validating duration inputs in survival analysis

ACTIONReject negative or zero durations with ValueError

CONSEQUENCENegative durations are mathematically invalid in survival analysis, causing incorrect hazard rate calculations and producing meaningless survival curves that misrepresent actual time-to-event distributions

WHENWhen processing event_observed array for survival models

ACTIONCast event_observed to integer type and then to boolean

CONSEQUENCEInvalid event values (non-0/1, non-boolean) will produce undefined behavior in likelihood calculations, potentially causing silent errors in survival function estimation

WHENWhen accepting user-provided DataFrame in fit() method

ACTIONCreate a shallow copy of the input DataFrame before extraction operations

CONSEQUENCEThe original DataFrame will be permanently modified by .pop() operations on duration/event/weights columns, corrupting user data and violating data isolation principles