Create a prior observation duration variable

Produces a derived variable computing days from observation start to a fixed reference date. When omitted, today's date is recorded in the variable specification at construction time. With multiple observation spells, the unique period containing the reference date is selected; no covering period yields a missing value and overlapping covering periods fail closed.

Usage

omop_variable_prior_obs(name = "prior_obs", reference_date = NULL)

Arguments

name

Character; output column name (default "prior_obs").

reference_date

Date or NULL; explicit reference date.

Value

An omop_variable with format = "prior_obs".