Clarifying the biological and statistical assumptions of cross-sectional biological age predictors: an elaborate illustration using synthetic and real data.

"availability of data and materials all r-code used for the analyses in this paper including the code used to generate the synthetic data is available in a public github repository ( https://github com/marije-sluiskes/cross-sectional-bioage )."

"availability of data and materials all r-code used for the analyses in this paper including the code used to generate the synthetic data is available in a public github repository ( https://github com/marije-sluiskes/cross-sectional-bioage )."

"Declarations Ethics approval and consent to participateThe study protocol of the Leiden Longevity Study was approved by the medical ethics committee of the Leiden University Medical Center before the start of the study. Informed consent was obtained from all participants prior to entering the study. All methods were carried out in accordance with relevant guidelines and regulations. Consent for publicationNot applicable. Competing interestsThe authors declare no competing interests. Competing interests The authors declare no competing interests."

"Funding The Leiden Longevity Study has received funding from the European Union’s Seventh Framework Programme (FP7/2007-2011) under grant agreement number 259679. The LLS was further supported by a grant from the Innovation-Oriented Research Program on Genomics (SenterNovem IGE05007), the Centre for Medical Systems Biology, and the Netherlands Consortium for Healthy Ageing (grant 050-060-810), all in the framework of the Netherlands Genomics Initiative, Netherlands Organization for Scientific Research (NWO), by BBMRI-NL, a Research Infrastructure financed by the Dutch government (NWO 184.021.007 and 184.033.111) and the VOILA Consortium (ZonMw 457001001). The funding bodies had no role in the design of the study, in the collection, analysis and interpretation of data, or in writing the manuscript."