These authors appear to have extracted out some statistical relationship from this data set. Torturing the data like this must be necessary to get a paper published, but it does not provide any new reliable information. At one time (long long ago) authors were much more careful when reporting statistical relationships. But being careful and precise does not generate funding. Given the 95% CI the PR would hardly qualify as having any practical significance, regardless of the PR reported. Surely there are more obvious and significant health issues than this where epidemiology studies would be useful. But more and more ecological studies of drinking water like this are not getting us anywhere.
Sanders AP, Desrosiers TA, Warren JL, Herring AH, Enright D, Olshan AF, Meyer RE, Fry RC. Association between arsenic, cadmium, manganese, and lead levels in private wells and birth defects prevalence in North Carolina: a semi-ecologic study. BMC Public Health. 2014 Sep 15;14(1):955.
BACKGROUND: Toxic metals including arsenic, cadmium, manganese, and lead are known human developmental toxicants that are able to cross the placental barrier from mother to fetus. In this population-based study, we assess the association between metal concentrations in private well water and birth defect prevalence in North Carolina.
METHODS: A semi-ecologic study was conducted including 20,151 infants born between 2003 and 2008 with selected birth defects (cases) identified by the North Carolina Birth Defects Monitoring Program, and 668,381 non-malformed infants (controls). Maternal residences at delivery and over 10,000 well locations measured for metals by the North Carolina Division of Public Health were geocoded. The average level of each metal was calculated among wells sampled within North Carolina census tracts. Individual exposure was assigned as the average metal level of the census tract that contained the geocoded maternal residence. Prevalence ratios (PR) with 95% confidence intervals (CI) were calculated to estimate the association between the prevalence of birth defects in the highest category (>=90th percentile) of average census tract metal levels and compared to the lowest category (<=50th percentile).
RESULTS: Statewide, private well metal levels exceeded the EPA Maximum Contaminant Level (MCL) or secondary MCL for arsenic, cadmium, manganese, and lead in 2.4, 0.1, 20.5, and 3.1 percent of wells tested. Elevated manganese levels were statistically significantly associated with a higher prevalence of conotruncal heart defects (PR: 1.6 95% CI: 1.1-2.5).
CONCLUSIONS: These findings suggest an ecologic association between higher manganese concentrations in drinking water and the prevalence of conotruncal heart defects.
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