Reject Self Fallback

Goal: fill SEVAL, the severity recorded at the visit, from the collected severity when present, otherwise from SEVAL itself, defaulting to 0 when neither gives a value.

Input: vital-sign records carrying study, subject, and sequence entries plus the collected severity (SEVAL), which is missing when no severity was recorded.

Variables:

• SEVAL: the collected severity when one was recorded at the visit, otherwise the value of SEVAL itself, otherwise 0. Because SEVAL reads its own value, there is no earlier value to carry and the definition loops back on itself, so the run is rejected before any data is read and no artifact is accepted.

How to fix

Carry forward from the collected source instead of the column being derived. Search the subject's earlier collected values in a separate column, and fall back to it, then to 0, only when the current record has no severity:

- name: SEVPREV
  type: int
  derivation:
    previous_non_missing:
      source: VS.SEVAL
      window:
        group_by: [STUDYID, USUBJID]
        order_by: [VSSEQ]

- name: SEVAL
  type: int
  derivation:
    first_available:
      sources: [VS.SEVAL, SEVPREV]
      missing: 0

Keep SEVPREV internal by omitting it from output.columns. A subject whose first record has no severity gets 0 there, because no earlier value exists.