Cohort time-zero alignment ========================== StatMedAnalysis | Original downloadable worksheet | 6 November 2026 Align eligibility, exposure assignment and follow-up start to prevent immortal-time errors. How to use this worksheet Draw a timeline for each exposure group using synthetic dates. Place eligibility assessment, treatment decision and first counted outcome risk on the same diagram. Identify any future information used to classify baseline exposure. Route time-varying strategies to an appropriate design instead of forcing a baseline label. Save a working copy and keep the original blank version. Use public, hypothetical or aggregate information only; do not enter patient identifiers, credentials or confidential records. Keep source evidence in your approved project workspace. Mark unresolved text fields UNKNOWN or NOT REPORTED with a reason; never substitute zero for an unknown count. Project/version __________________ Prepared by role/date __________________ Working fields 1. Eligibility assessment date rule Response/evidence: _________________________________________________________ ___________________________________________________________________________ 2. Treatment assignment rule Response/evidence: _________________________________________________________ ___________________________________________________________________________ 3. Follow-up entry rule Response/evidence: _________________________________________________________ ___________________________________________________________________________ 4. Future information used for classification Response/evidence: _________________________________________________________ ___________________________________________________________________________ 5. Events before classification Response/evidence: _________________________________________________________ ___________________________________________________________________________ 6. Grace-period handling Response/evidence: _________________________________________________________ ___________________________________________________________________________ 7. Comparison timeline Response/evidence: _________________________________________________________ ___________________________________________________________________________ 8. Redesign decision and owner Response/evidence: _________________________________________________________ ___________________________________________________________________________ Hypothetical worked case In a fictional study, users are defined by receiving a prescription within 90 days after diagnosis, but follow-up starts at diagnosis. Survival to prescription is required to become a user; that period cannot simply be assigned to exposed baseline time. Decision rule and limitations Hold the analysis when exposure classification requires survival after its proposed baseline. Correct the design and rederive follow-up before fitting an adjusted model. Decision _______________________ Remaining uncertainty ____________________ Next action ____________________ Owner / review date ______________________ Independent check and discrepancy resolution _______________________________ Official method or reporting reference checked 6 November 2026 https://miguelhernan.org/whatifbook This is an original planning aid, not an official checklist, validated instrument, clinical recommendation or certificate of expert approval. Apply the referenced guidance to the specific design and record any additional requirements.