I think people are mistaken in thinking that anything published in a reputable source can be considered a reliable source unless it is clear that source has some kind of expertise or reputation for reporting those kind of facts accurately I do not believe the Guardian Observer or any other newspaper check statements made about people s ancestry for reliability therefore I do not believe that they can be considered a reliable source in this context Only sources that have some kind of expertise and are known to do detailed research should be considered reliable for such purposes i e The Jewish Year Book or Jewish Chronicle