Is anecdotal evidence dangerous?

[nereas]

For NDL diving you can pretty much play any game you want, whether to make any particular set of dive tables your gospel, and push their limits as far as you dare anecdotally. Worst case is that you would then earn a chamber ride. Make sure your DAN insurance is paid, first though.

For deco diving, you cannot take anything for granted nor delude yourself, however; the penalty then is paralysis or death. You must start with a fairly shallow (150 fsw) dive for a fairly short time (20 mins), and test whatever table or software you are using from that point on with your own unique body and all of its hidden biological flaws. The anecdote then becomes one of conservatism, not of pushing your limits. It also helps if you dive optimal gasses and extend your deco times.

It was my honor to hear from Thal offline about his own guarded reservations about USN tables at their extremes. And it was my pleasure to see Geoff backpedalling from his fantasy logic when the proof was in the pudding.

Anyone still seeking the holy grail of "scientific" tables without anecdote might as well be looking for the golden fleece as well. Dave, I think your heart is in the right place about following a conservative scientific catechism. I just do not believe there are any that exist which are valid. Certainly not across the board, not for everybody.

Maybe Thal is super-human and can get away with anything? So what? I'm not going to try it.

 

[Thalassamania]

Maybe Thal is super-human and can get away with anything? So what? I'm not going to try it.

Quite the opposite, in fact a group of us in the operations team for the Deep Rover submersible were know as the "SUBhumans." Seriously, the U.S. Navy tables are, without question the best tested set of tables that there has ever been. At first blush, when you're talking about a single no-decompression dive, you can say, "well why not dive them one step or two steps back?" That's fine for one dive a day but when you get into repetitive diving that really does not work. I need to know where the edge is so that I don't step over it ... not that there is some crumbly slope somewhere over there. Besides, by the time you figure the U.S. Navy square dive vs. the actual profile and the factor added for cold and exertion, you're diving pretty conservative.

 

[The Chairman]

Anyone still seeking the holy grail of "scientific" tables without anecdote might as well be looking for the golden fleece as well. Dave, I think your heart is in the right place about following a conservative scientific catechism. I just do not believe there are any that exist which are valid. Certainly not across the board, not for everybody.

Maybe Thal is super-human and can get away with anything? So what? I'm not going to try it.

I fully concur.

 

[Laruuk]

After reading this entire thread, All I have to say is ...

... my brain hurts.

 

[The Chairman]

After reading this entire thread, All I have to say is ...

... my brain hurts.

Glancing at your avatar explains that, albeit anecdotal in nature.

 

[Geoff_H]

And it was my pleasure to see Geoff backpedalling from his fantasy logic when the proof was in the pudding.

I'm just back from the weekend's diving and I was surprised to read this since I remember doing nothing of the sort. A quick check back in the thread proves the point.

But, feel free to set up any more strawmen and knock them down if that's what floats your boat.

 

[spydeedyves]

I feel that it can be just as dangerous to assume that science will always keep you safe. There are plenty examples of highly skilled divers following scientific, conservative diving practices that still get bent without any obvious reason. Part of the scientific equation involves the use of subjects. Vary the subject...vary the results. Even our own bodys can be different from day to day and that will change how scientific principals apply.

The best approach, IMHO, is to learn your own limitations, slowely and at a safe pace. Strive to do more and to go further with the intent of learning your limitations and not for the reason of breaking records, meeting challenges or impressing others. Use the science as a guide and not a bible and let common sense prevail.

Extremely well-put. I believe in safe practices, education and the application of tried principles. I don't support dogma of any kind, but I would never ever rely solely on the statements of one person who is different from me physically, emotionally and whose experience differs from my own.

 

[bfw]

The problem with anecdotal evidence is that it is tainted by personal view and not supported by emperical evidence gathered in a scientific controlled environment.

No, the problem is statistical sample size. Anecdotal evidence may be completely objective and verifiable, but it's a single datum, or, at best, a few data points. You can't demonstrate a correlation, let alone causation, for n = 1. You can't establish a reliable principle with a single observation, because you haven't established that it's repeatable.

Anecdotal evidence is not completely without value. A single datum is sufficient to rebut a blanket generalization - any statement involving the terms "always" or "never" can be disproved with a single verifiable counter-example. Of course, when dealing with the dynamics of human performance, as most dive safety/training questions do, it's very probable that the generalization was ridiculous to begin with, and thus no one who cares about valid proofs took it seriously anyway.

 

[MaxBottomtime]

All one has to do is search the word nitrox on Scubaboard. Despite the fact that there is only anecdotal evidence, you will find at least half the posters swearing that nitrox gives them more energy or is safer than air. Even the nitrox courses tell you that it only extends no-deco limits and shortens required surface intervals, yet people want to believe the anecdotes.

 

[Rhone Man]

All one has to do is search the word nitrox on Scubaboard. Despite the fact that there is only anecdotal evidence, you will find at least half the posters swearing that nitrox gives them more energy or is safer than air.

Nitrox also give me the power to fly, read minds and tell the future....

Seriously though, I think there is more than mere anecdotal evidence to support the notion that nitrox gives you more energy after a dive. I was reading a good article in a British diving magazine on exactly this point recently: After a dive of any significant depth and/or duration, you are going to get micro bubbles in your bloodstream as the nitrogen comes out of solution, and this inhibits the blood's way of moving oxygen around the body (not wholly dissimilar to leukemia, but obviously much less nasty), hence the tired feeling after diving. Nitrox means less nitrogen absorbed by the body, hence less micro bubbles coming out of solution, hence less latent tiredness. Interestingly the other thing that the article recommended for reducing tiredness was "deep stops", beloved of technical divers, but still a rarity in the recreational diving world. I meant to start a thread on that very subject, but never got around to it. I'll see if I can dig up the article and start a thread to give the topic a good airing (ha - pun!).