Type O negative here who has had three years of gains in the market. I am inclined to think that if the majority of investors lost money in a down market, the poll numbers would look much different in a good market with agressive blood types making more $.
I think you're right.
Your blood is the most valuable!
I'd be more interested in this study if they did the breakdown of the commonality of various types. For instance, my type, B+ apparently originated in Asia. Too bad I stink in investments according to the study.