What often happens is that A) a study is too small, or B) A study is flawed. That's why, in science, one study is never enough. Both of these happen fairly frequently. There's also a very common problem with certain very common type of study which by its very nature, can be both flawed and biased, despite the best intentions of the researchers. What happens is that a researcher gets a brilliant idea that in order to work around a problem of insufficient data, they compile numbers from multiple sources into a single report. But people keep making this same mistake. The problem with it is two-fold. First, there's always an inherent bias towards reproducing the original results, simply because when people try to reproduce the results, and fail, those studies will often not get published (or, if the results of the original study are surprising, the exact opposite can happen). Secondly, the methodology for various studies can vary to a large extent so that you may actually be combining apples and oranges. Anyway, science takes time, and it takes repetition, and it takes a lot of scrutiny and peer review and questioning. Without all of that, a single study doesn't amount to much.
The world is flat, and we will drive our flying cars to work on the Moon in another decade. I.E. Common opinions do not mean correct opinions. I could spew hundreds of examples of where the vast majority of the world believed one thing and it was later proven false. Mercury, lead, and wood alcohol come to mind, but this is all off the real topic here. The purpose of this post is to say that while everything Haldurson said about studies is correct, it is even worse than that. When an obviously flawed study is released, if it supports a common belief, people will reinforce it and be resistant to it being questioned. People were called fools or worse for daring to question the flatness of the Earth. Proper, double-blind studies are essential. If for nothing else but to confirm the things we believe to be correct. And skepticism should always go both ways. If someone questions our history and knowledge, we should welcome the exploration of the known. (Unless it is this guy.) I know... I am a hypocrite. But I actually *DID* watch the several hours of videos this 'loon presented. He is in my never humble opinion, wrong.
