prev_visit_at_threshold: Determine which visits for any subject occur after C-peptide...

In mjdufort/CpeptideTools: Tools for handling C-peptide data from MMTT/OGTT

Determine which visits for any subject occur after C-peptide AUC has reached the detection limit

Description

This function determines which visits (if any) for each subject occur after that subject's C-peptide AUC has reached the detection limit. This function is intended to be used to filter out such visits, to prevent violations of the linearity assumption in the model fitting for slope estimation. For AUC values, it's assumed that the AUC has reached the detection limit when means the C-peptide levels for each timepoint in the MMTT or OGTT are at the detection limit; the AUC detection limit should be calculated as such. As input, the function takes a data frame of C-peptide values, with subject identifiers and a date or visit column on which to sort the visits. Note that visits will be sorted blindly, so character visit names (e.g. Day 1, Week 1, Month 2) should be used with EXTREME CAUTION! Numeric, date, or factor visit values are strongly preferred.

Usage

prev_visit_at_threshold(
  cpeptide_auc_data, threshold,
  identifier_column = "subject", sort_column = "visit",
  auc_column = "auc")

Arguments

cpeptide_auc_data	data frame containing the C-peptide data. Should contain a unique subject identifer, a column for sorting visits, and the C-peptide AUC data. Each row should be a single visit.
threshold	numeric, the threshold C-peptide AUC value. Values at or below this level will be treated as sub-threshold.
identifier_column	character or numeric, the column containing the subject identifiers. By default it uses "subject".
sort_column	character or numeric, the column on which each subject's visits should be sorted. This should be either numeric, date, or character that will be sorted consistently by dplyr::arrange(). If set to NULL, rows for each subject will be assumed to be in the desired order. By default it uses "visit".
auc_column	character or numeric, the column containing the C-peptide AUC values. By default it uses "auc".

Value

a logical vector, with each element corresponding to a row of the input data frame; contains TRUE if the subject already had C-peptide AUC at or below the threshold at prior visits, and FALSE otherwise.

mjdufort/CpeptideTools documentation built on March 5, 2025, 6:58 p.m.