Well the article on the University's web-page states the study was commissioned ...

Well the article on the University's web-page states the study was commissioned by the municipality of Alphen aan der Rijn. The municipality's website has two pages about the study: http://www.alphenaandenrijn.nl/Smartsite.shtml?id=75994 http://www.alphenaandenrijn.nl/Smartsite.shtml?id=63643

The second one, at least, refers to a control group. The first suggests contacting the author for further details. I think it is a case where the news value of a piece of research outruns the peer review and publication process. For all we know the author thinks a lot more research is needed before he can publish anything.