Link: http://www.ncbi.nlm.nih.gov/pubmed/25155701

Paediatr Perinat Epidemiol. 2014 Sep;28(5):424-33. doi: 10.1111/ppe.12140. Epub 2014 Aug 26.
Using bayesian models to assess the effects of under-reporting of cannabis use on the association with birth defects, national birth defects prevention study, 1997-2005.
van Gelder MM1, Donders AR, Devine O, Roeleveld N, Reefhuis J; National Birth Defects Prevention Study.
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Abstract
BACKGROUND:
Studies on associations between periconceptional cannabis exposure and birth defects have mainly relied on self-reported exposure. Therefore, the results may be biased due to under-reporting of the exposure. The aim of this study was to quantify the potential effects of this form of exposure misclassification.
METHODS:
Using multivariable logistic regression, we re-analysed associations between periconceptional cannabis use and 20 specific birth defects using data from the National Birth Defects Prevention Study from 1997-2005 for 13 859 case infants and 6556 control infants. For seven birth defects, we implemented four Bayesian models based on various assumptions concerning the sensitivity of self-reported cannabis use to estimate odds ratios (ORs), adjusted for confounding and under-reporting of the exposure. We used information on sensitivity of self-reported cannabis use from the literature for prior assumptions.
RESULTS:
The results unadjusted for under-reporting of the exposure showed an association between cannabis use and anencephaly (posterior OR 1.9 [95% credible interval (CRI) 1.1, 3.2]) which persisted after adjustment for potential exposure misclassification. Initially, no statistically significant associations were observed between cannabis use and the other birth defect categories studied. Although adjustment for under-reporting did not notably change these effect estimates, cannabis use was associated with esophageal atresia (posterior OR 1.7 [95% CRI 1.0, 2.9]), diaphragmatic hernia (posterior OR 1.8 [95% CRI 1.1, 3.0]), and gastroschisis (posterior OR 1.7 [95% CRI 1.2, 2.3]) after correction for exposure misclassification.
CONCLUSIONS:
Under-reporting of the exposure may have obscured some cannabis-birth defect associations in previous studies. However, the resulting bias is likely to be limited.
? 2014 John Wiley & Sons Ltd.
KEYWORDS:
Anencephaly; Bayes theorem; Bias (epidemiology); Birth defects; Cannabis; Diaphragmatic hernia; Epidemiologic methods; Esophageal atresia; Gastroschisis; Maternal exposure
Comment in
Importance of bias analysis in epidemiologic research. [Paediatr Perinat Epidemiol. 2014]
PMID: 25155701 [PubMed - indexed for MEDLINE] PMCID: PMC4532339 Free PMC Article