If you don’t have a Ph.D. (or its educational equivalent), you shouldn’t consider yourself a serious researcher. The Ph.D. degree prepares (and qualifies) you to do solid empirical research that can stand up to peer-review.
You can certainly do science with any degree (heck, you don’t even need a degree to do science!), so naturally medical doctors (M.D.s) can do science. But it’s also why you see the really serious medical researchers go on and get a Ph.D. as well. The Ph.D. provides the deep didactic training in research methods and statistics you need to actually do serious research, not just interpret it.
That’s why I’m not a serious researcher — I know my limitations. I can interpret research until the cows come home, but I do very little of it myself.
That’s also why it was enjoyable reading Vaughan Bell’s post over at Mind Hacks about neuropsychiatrist’s Louann Brizendine new article over at CNN (which apparently doesn’t bother do any editorial vetting of the content it publishes). In the blog entry, Bell points out at least one ridiculous contention Brizendine makes in the CNN piece.