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However, these data often contain measurement error and excess zeros (due to nonwear, sedentary behavior, or connectivity issues), each characterized by subject\u2010specific distributions. Current statistical methods fail to address these issues simultaneously. We introduce a novel modeling framework for zero\u2010inflated and error\u2010prone functional data by incorporating a subject\u2010specific time\u2010varying validity indicator that explicitly distinguishes structural zeros from intrinsic values. We iteratively estimate the latent functional covariates and zero\u2010inflation probabilities via maximum likelihood, using basis expansions and linear mixed models to adjust for measurement error. To assess the effects of the recovered latent covariates, we apply joint quantile regression across multiple quantile levels. Through extensive simulations, we demonstrate that our approach significantly improves estimation accuracy over methods that only address measurement error, and joint estimation yields substantial improvements compared with fitting separate quantile regressions. Applied to a childhood obesity study, our approach effectively corrects for zero inflation and measurement error in step counts, yielding results that closely align with energy expenditure and supporting their use as a proxy for physical activity.<\/jats:p>","DOI":"10.1002\/sim.70598","type":"journal-article","created":{"date-parts":[[2026,5,15]],"date-time":"2026-05-15T05:50:09Z","timestamp":1778824209000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Correcting Measurement Error and Zero Inflation in Functional Covariates for Scalar\u2010on\u2010Function Quantile Regression"],"prefix":"10.1002","volume":"45","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9529-0500","authenticated-orcid":false,"given":"Caihong","family":"Qin","sequence":"first","affiliation":[{"name":"Department of Epidemiology and Biostatistics School of Public Health, Indiana University  Bloomington Indiana 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