The scientific method can be a powerful tool for weighing the evidence & exploring for truth. But it's not perfect, particularly as applied by humans (often paid for by an agency with a stake in the results, performed by researchers with expectations, etc...). The quality of research varies widely (e.g.: should we assume chamber dives are a reliable representative of actual dives? Should the chamber folks be doing exercises to more closely match real divers?). Even studies that look good are sometimes 'disproven' (or at least contradicted) by later studies. And the scientific community tries to err on the side of avoiding false positive findings. For example, the standard I was taught is that statistical testing to determine whether a finding (difference between study groups) is statistically (may not be of practical importance) significant is to determine whether the odds of random chance accounting for the findings is no more than 5%.
RJP already outlined the serious hardships that would be faced in implementing a rigorous prospective double-blind placebo controlled scientific study reasonably expected to show a difference (if there is one) & r/o random chance to the level of being under 5% likely to account for that difference.
So we may never get the 'scientific evidence' that nitrox helps a significant portion (even if a minority) of divers feel better.
While we don't want to see nitrox peddled as a modern day 'snake oil,' at the same time be mindful much of what we experience and deem true in life has not been substantiated by scientific research & published in a peer reviewed journal. If I stump my toe, it hurts. My experience of that is anecdotal; I haven't seen an article showing that's been proven. Do I just
think it hurts? No; I know it does. Put another way, imagine that you refused to believe
anything that had not been scientifically established in a peer reviewed professional journal. You'd be too ignorant to function in daily life.
Let's take a look at some description from some research links RJP posted:
In this double blinded, randomized controlled study 11 divers breathed either air or Enriched Air Nitrox 36% (oxygen 36%, nitrogen 64%) during an 18 msw (281 kPa(a)) dry chamber dive for a bottom time of 40 minutes. Two periods of exercise were performed during the dive. Divers were assessed before and after each dive using the Multidimensional Fatigue Inventory-20, a visual analogue scale, Digit Span Tests, Stroop Tests, and Divers Health Survey (DHS). Diving to 18m produced no measurable difference in fatigue, attention levels, ability to concentrate or DHS scores, following dives using either breathing gas.
One dive? Chamber? Only 11 divers?
The purpose of this double-blind study was to compare subjective fatigue levels experienced by SCUBA divers after two repetitive air dives and two repetitive EAN36 dives on separate, nonconsecutive days. Eleven male participants completed pre- and post-dive fatigue assessment using the Multidimensional Fatigue Inventory and a Visual Analogue Scale, while general health was assessed using the Diver Health Survey. Divers did tend to be more fatigued after diving; however, breathing gas mixture exhibited no statistically significant effect. Participants did have significantly lower Diver Health Survey scores upon the conclusion of EAN36 test sessions, possibly indicative of reduced decompression stress.
2 Dives? And still just 11 people.
Seems to me we need people diving more like instructors teaching classes or people shore diving Bonaire (e.g.: exercising & mentally stimulated teaching students, or hauling gear around & walking in & out), and doing something more like 5 or 6 dives per day for a few days running.
Someone in an older thread debating this issue compared it to doing a study of whether beer is more likely to be intoxicating than root beer, and giving your study groups just one glass. Then, when one beer makes nobody drunk, claiming your study shows no difference.
Richard.
