Extrapolate missing sigma values for age-to-age links

Internal helper that fills NA or non-positive sigma values in a filtered ata factor table. Five methods are supported: "locf", "min_last2", "loglinear", "mack", and "none". See Details.

Usage

.extrapolate_sigma_ata(
  x,
  method = c("locf", "min_last2", "loglinear", "mack", "none")
)

Arguments

x

A data.table with ata_from and sigma columns, typically the output of .filter_ata().

method

One of "locf" (default), "min_last2", "loglinear", "mack", or "none". "mack" applies Mack (1993) Appendix B tail estimator to the last unestimated link only and falls back to LOCF for any earlier unestimated links with a warning. "none" performs no extrapolation and leaves sigma as NA; downstream variance terms then drop those links via finite-value guards.

Value

A data.table with missing sigma values filled and a new logical column sigma_extrapolated flagging imputed rows.