A Duke University study published in the Proceedings of the National Academy of Sciences titled, "Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction". The study supposedly shows a connection between natural gas drilling and stray gas (mostly methane) in nearby water wells. This is the second time Duke has published such a study. The study from 2011 was criticized for funding by the anti-drilling Park Foundation and for its weak research methodology. This second study has also come under fire for some of the same weaknesses.