Our hobby certainly has its share of unsubstantiated lore, but I don't think that this fits in that category.
Vic in Va posted a graph from two very reputable sources, Floyd Brownell and Harold Vaughn. So I think that there is data to support the idea. I have both of their publications, and do remember seeing the graph.
It would be very interesting to compare the USMC data, and see if we can figure out why we have the discrepancy.
