Confounding Underlies the Apparent Month of Birth Effect in Multiple Sclerosis
نویسندگان
چکیده
OBJECTIVE Several groups have reported apparent association between month of birth and multiple sclerosis. We sought to test the extent to which such studies might be confounded by extraneous variables such as year and place of birth. METHODS Using national birth statistics from 2 continents, we assessed the evidence for seasonal variations in birth rate and tested the extent to which these are subject to regional and temporal variation. We then established the age and regional origin distribution for a typical multiple sclerosis case collection and determined the false-positive rate expected when comparing such a collection with birth rates estimated by averaging population-specific national statistics. RESULTS We confirm that seasonality in birth rate is ubiquitous and subject to highly significant regional and temporal variations. In the context of this variation we show that birth rates observed in typical case collections are highly likely to deviate significantly from those obtained by the simple unweighted averaging of national statistics. The significant correlations between birth rates and both place (latitude) and time (year of birth) that characterize the general population indicate that the apparent seasonal patterns for month of birth suggested to be specific for multiple sclerosis (increased in the spring and reduced in the winter) are expected by chance alone. INTERPRETATION In the absence of adequate control for confounding factors, such as year and place of birth, our analyses indicate that the previous claims for association of multiple sclerosis with month of birth are probably false positives.
منابع مشابه
Month of birth and risk of multiple sclerosis: confounding and adjustments
A month of birth effect on multiple sclerosis (MS) risk has been reported from different countries. Recent critics have suggested that this finding is caused by confounding and that adequately adjusting for year and place of birth would markedly reduce this effect. All inhabitants in Norway are registered in the Norwegian Population Registry (Statistics Norway), making this an ideal area for pe...
متن کاملComment on: Month of birth and risk of multiple sclerosis: confounding and adjustments
We read the latest paper from Torkildsen et al. with great interest and agree with the authors that their data provide a convincing empirical demonstration of the extent to which failing to correct for year and place of birth can generate false-positive associations in studies considering the role of month of birth (MOB) in multiple sclerosis. However, regarding their suggestion that these data...
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Passive smoking (PS), a well-known health risk, is the major source of indoor pollution. There is some inconsistent evidence that PS during pregnancy may increase the risk of low birth weight. The aim of the present study was to determine the effects of PS exposure during pregnancy on weight, length and cranial circumference at birth of babies born to women who have described themselves ...
متن کاملReply to comment: Month of birth and risk of multiple sclerosis: confounding and adjustments
Reply to comment: Month of birth and risk of multiple sclerosis: confounding and adjustments Øivind Torkildsen*, Jan Aarseth, Elisabeth Gulowsen Celius, Trygve Holmøy, Margitta T. Kampman, Kristin Ingeleiv Løken-Amsrud, Rune Midgard, Kjell-Morten Myhr, Trond Riise & Nina Grytten Norwegian Multiple Sclerosis Competence Centre, Department of Neurology, Haukeland University Hospital, Bergen, Norwa...
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