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The multivariate model forPTA3,4,6 only explains 41.1% of the variance in hearingthreshold levels; hence, most of the variation is notexplained by variables measured in this study. Otherstudies performing multiple regression analyses to examinethe effect of noise exposure and hearing ability adjusted forseveral confounders, found smaller R2for their multivariatemodels of 30.6% (Agrawal et al. 2010) and 36% (Toppilaet al. 2000).Differences in the inpidual susceptibility to noise maybe responsible for the large spread of inpidual thresholdvalues. Several possible explanatory variables that hypo-thetically could be responsible for part of the variance,such as medical history, non-occupational noise exposureand drug usage, are not included in these analyses, becauseof a lack of information concerning these factors.ConclusionThis analysis of a large audiometric dataset show thatDutch construction workers exhibit greater hearing lossesthan expected based solely on ageing. Accumulation of theinevitable age-related hearing loss may result in moderateto severe hearing impairment at retirement age.Regression models show a great inter-inpidual vari-ability in reported hearing loss, and only a weak relation-ship between noise level and hearing ability is found. Atlow noise exposure levels, hearing loss is much greaterthan predicted whereas at high levels hearing loss is less.This latter might be partly explained by the role of personalhearing protection, which is worn by a greater proportionof highly exposed workers than workers exposed to lowernoise levels. Inpidual noise exposure level measurementscan increase the accuracy of the noise intensity estimatesand results in a more reliable estimate of this relationship.Growth of hearing loss with progressing exposure timeis in accordance with ISO predictions for exposure dura-tions between 10 and 40 years. However, the interpolationdescribed in the ISO model that predicts hearing lossdeveloped during the first 10 years of exposure is notconsistent with our data and seems to be inapplicable inthis population. Our hypothesis is that pre-existing hearingloss from non-occupational noise exposure is the mostimportant explanation for this inconsistency.In a follow-up study, personal dosimetry and extensiveinformation on job history should be taken into accountestimating noise exposure levels. In addition, serial audi-ometry with a baseline measurement at job entrance shouldbe performed and more detailed information should becollected about factors influencing hearing ability, such as,non-occupational noise exposure, medical history anddetails of hearing protector usage.Acknowledgments The authors acknowledge Arbouw for the col-lection and management of all occupational health-related data.Special thanks to Hiske Helleman and Noortje Jansen for theirassistance with data analysis. This research was funded by Arbouw.Conflict of interest The authors declare that they have no conflictof interest.Open Access This article is distributed under the terms of theCreative Commons Attribution Noncommercial License which per-mits any noncommercial use, distribution, and reproduction in anymedium, provided the original author(s) and source are credited.ReferencesAgrawal Y, Niparko JK, Dobie RA (2010) Estimating the effect ofoccupational noise exposure on hearing thresholds: the impor-tance of adjusting for confounding variables. Ear Hear311:234–237ANSI S 3.44 (1996) Determination of occupational noise exposureand estimation of noise-induced hearing impairment. AmericanNational Standards Institute, New YorkArbouw (2009) Bedrijfstakatlas 2009. Stichting Arbouw, HarderwijkArndt V, Rothenbacher D, Brenner H, Fraisse E, Zschenderlein B,Daniel U, Schuberth S, Fliedner TM (1996) Older workers in theconstruction industry: results of a routine health examination anda five year follow up. Occup Environ Med 53:686–691Bauer P, Ko ¨rpert K, Neuberger M, Raber A, Schwertz F (1991) Riskfactors for hearing loss at different frequencies in a population of47.388 noise-exposed workers. J Acoust Soc Am 90:3086–3098Davies H, Marion S, Teschke K (2008) The impact of hearingconservation programs on incidence of noise-induced hearingloss in Canadian workers.