Calendar duration and protocol-day audit
Method review date: 2026-11-03

Instructions: Save a copy, complete blanks and record unresolved questions. Use fictional or aggregate values only; never patient identifiers. This planning aid does not certify an analysis.

DEFINE DATES BEFORE SUBTRACTING
Meaning/source of start: ____; end: ____
Recorded as full civil date or timestamp? ____
Calendar: ____; timezone if timestamps: ____
Partial/ambiguous/invalid dates and handling: ____

CHOOSE CONVENTION
Start date (YYYY-MM-DD): ____; end date: ____
Elapsed civil calendar days (same date=0): ____
Inclusive dates counted (same date=1): ____
If start is day 0, end-day index: ____
If start is day 1, end-day index: ____
Protocol-specified convention and source section: ____

TEST BOUNDARIES WITH FICTIONAL DATES
Same-date case and expected count: ____
Leap-year crossing: ____
Month/year crossing: ____
Reversed dates should flag an error: ____
Check 1900 is not a leap year and 2000 is.
Civil-day counts are not elapsed 24-hour periods between local timestamps.

APPLY WITHOUT INVENTING RULES
Weekends/holidays, anniversaries and visit windows require separate rules: ____
Independent calculation and software/date-parser version: ____
Off-by-one check against protocol examples: ____
Unresolved records, correction history and approved derivation: ____

Practical guide: https://www.statmedanalysis.com/blog/protocol-day-indexing
Project/version: ____  Completed by role/date: ____