Don,
The chart that I posted came from here:
re: The Relative Risk of SCUBA Diving
The other information came from other places that I can't find again without repeating the work. I didn't keep source notes. I can tell you that I was looking at wiki, and all of their links, especially in RE to mortality rates for driving, some links were quoting DoT stats, some websites looked to be insurance company related (both mostly from the US.) As I said in my former post, I wouldn't give any of those sources a ton of credence. I'm a bit of an old fashioned academic, and internet sighting, without firm sourcing is sort of a no-no to me, which is why I stated to take it for what it was worth. I do know one of the Google searches that I did was "comparative mortality rates," and I went a good 10 - 15 pages into links to try and find some that were breaking it down by hours spent in activity so I could, at least somewhat, compare apples to apples. Other information also came from people that were quoting DAN, including a lot of links to ScubaBoard. But again, I wouldn't take any of that for Gospel.
All I can tell you is that from what I was able to piece together, IMO as it were, it appeared to me from at least 4 different approaches that the 4x factor seemed to be relatively consistent. However, at the end of the day I didn't seem to find anything that I would call reliable, academically approachable, global stats that would be definitive.
As I originally stated though, even at 4x more "dangerous" I wouldn't trade spending time with my son diving for something less dangerous. The memories and experiences we share diving together here in Curacao will be things that we cherish for a lifetime.
Safe diving,
Jeff