title: Calibration and seasonal adjustment for matched case-control studies of vitamin D and cancer.
abstract: Vitamin D measurements are influenced by seasonal variation and specific assay used. Motivated by multicenter studies of associations of vitamin D with cancer, we formulated an analytic framework for matched case-control data that accounts for seasonal variation and calibrates to a reference assay. Calibration data were obtained from controls sampled within decile strata of the uncalibrated vitamin D values. Seasonal sine-cosine series were fit to control data. Practical findings included the following: (1) failure to adjust for season and calibrate increased variance, bias, and mean square error and (2) analysis of continuous vitamin D requires a variance adjustment for variation in the calibration estimate. An advantage of the continuous linear risk model is that results are independent of the reference date for seasonal adjustment. (3) For categorical risk models, procedures based on categorizing the seasonally adjusted and calibrated vitamin D have near nominal operating characteristics; estimates of log odds ratios are not robust to choice of seasonal reference date, however. Thus, public health recommendations based on categories of vitamin D should also define the time of year to which they refer. This work supports the use of simple methods for calibration and seasonal adjustment and is informing analytic approaches for the multicenter Vitamin D Pooling Project for Breast and Colorectal Cancer. Published 2016. This article has been contributed to by US Government employees and their work is in the public domain in the USA.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, MD, U.S.A.
authors.forename: Mitchell H
authors.identifier: 0000-0002-9705-0842
authors.initials: MH
authors.lastname: Gail
authors.affiliation: Division of Biostatistics, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD, U.S.A.
authors.forename: Jincao
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.|Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.
authors.forename: Molin
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.
authors.forename: Shiaw-Shyuan
authors.initials: SS
authors.lastname: Yaun
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.|Division of Preventive Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, U.S.A.
authors.forename: Nancy R
authors.initials: NR
authors.lastname: Cook
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.|Channing Division of Network Medicine, Department of Medicine, Brigham and Womens Hospital and Harvard Medical School, Boston, MA, U.S.A.
authors.forename: A Heather
authors.initials: AH
authors.lastname: Eliassen
authors.affiliation: Epidemiology Research Program, American Cancer Society, Atlanta, GA, U.S.A.
authors.forename: Marjorie L
authors.initials: ML
authors.lastname: McCullough
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, MD, U.S.A.
authors.forename: Kai
authors.initials: K
authors.lastname: Yu
authors.affiliation: Department of Population Health and Perlmutter Cancer Center, New York University School of Medicine, New York, NY, U.S.A.
authors.forename: Anne
authors.initials: A
authors.lastname: Zeleniuch-Jacquotte
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.|Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA, U.S.A.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Smith-Warner
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, MD, U.S.A.
authors.forename: Regina G
authors.initials: RG
authors.lastname: Ziegler
authors.affiliation: Department of Statistics, Texas A&M University, College Station, TX, U.S.A.|Department of Mathematics and Statistics, University of Technology, Sydney, Australia.
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Carroll
mesh_terms: D001943:Breast Neoplasms / Q000097:blood / Q000453:epidemiology; D002138:Calibration; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000097:blood / Q000453:epidemiology; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D015233:Models, Statistical; D009369:Neoplasms / Q000097:blood / Q000453:epidemiology*; D012307:Risk Factors; D012621:Seasons; D013223:Statistics as Topic; D014807:Vitamin D / Q000097:blood*; D014815:Vitamins / Q000097:blood*
chemical_list: D014815:Vitamins; D014807:Vitamin D
keywords: biomarkers; calibration; matched case-control study; measurement error; molecular epidemiology; seasonal adjustment