Seasonality, mediation and comparison (SMAC) methods to identify influences on lung function decline

Emrah Gecili, Anushka Palipana, Cole Brokamp, Rui Huang, Eleni Rosalina Andrinopoulou, Teresa Pestian, Erika Rasnick, Ruth H. Keogh, Yizhao Ni, John P. Clancy, Patrick Ryan, Rhonda D. Szczesniak*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Downloads (Pure)


This study develops a comprehensive method to assess seasonal influences on a longitudinal marker and compare estimates between cohorts. The method extends existing approaches by (i) combining a sine-cosine model of seasonality with a specialized covariance function for modeling longitudinal correlation; (ii) performing mediation analysis on a seasonality model. An example dataset and R code are provided. The bundle of methods is referred to as seasonality, mediation and comparison (SMAC). The case study described utilizes lung function as the marker observed on a cystic fibrosis cohort but SMAC can be used to evaluate other markers and in other disease contexts. Key aspects of customization are as follows. • This study introduces a novel seasonality model to fit trajectories of lung function decline and demonstrates how to compare this model to a conventional model in this context. • Steps required for mediation analyses in the seasonality model are shown. • The necessary calculations to compare seasonality models between cohorts, based on estimation coefficients, are derived in the study.

Original languageEnglish
Article number101313
Publication statusPublished - 21 Mar 2021

Bibliographical note

Funding Information:
This work was supported by Grant R01 HL141286 from the National Institutes of Health and Grant GECILI20F0 from the Cystic Fibrosis Foundation . The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the Cystic Fibrosis Foundation. We thank the people with cystic fibrosis and their families who contributed the data which motivated these methodologic developments.

Publisher Copyright: © 2021


Dive into the research topics of 'Seasonality, mediation and comparison (SMAC) methods to identify influences on lung function decline'. Together they form a unique fingerprint.

Cite this