By how it works for you and how your kids come out? There is lots of research to back up attachment parenting--especially certain aspects like baby wearing and breastfeeding. . .I am a big
Dr. Sears fan personally, but if you are really looking for independent research you can look up baby wearing, co-sleeping and breastfeeding. . .to name a few and you'll come up with lots of information.
But honestly, I think most people fall into attachment parenting (or any parenting style) bc it makes sense for them and their families. They do what comes instinctively and what seems to be working and before they know it they find that most of their techniques fall into a certain 'style'. I know for us breastfeeding was a given. Well my oldest dd liked to eat all the time so we started co-sleeping so that I could get some sleep, and then someone gave me a sling bc she didn't like to be put in a stroller. . .and then I read a Dr. Sears book and a few more books and just kept doing what worked and what made sense to me.