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Survivor Bias

Discussion in 'Basic Scuba Discussions' started by jvogt, Oct 18, 2020.

  1. jvogt

    jvogt ScubaBoard Sponsor ScubaBoard Sponsor

    # of Dives: 200 - 499
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    Yesterday after reading this thread,

    Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

    I went for a mountain bike ride as it was an absolutely beautiful fall day hear in CO. I am a 30 year veteran of the sport and even spent a few years racing in the pro cross country field regionally. At one point I was in full confidence of my abilities going 30mph down a steep rocky slope on a narrow single track while wearing nothing but spandex and a foam bucket on my head. The thought popped into my head, is this survivor bias or experience? How does one know? I certainly haven't made it through my entire biking career unscathed. I have been in the hospital multiple times, and I have had friends that died. So what is the answer? When is someone assumed to know what they are doing? How does one know the difference between skill and ignorance?
     
    eleniel, Ana, OTF and 8 others like this.
  2. JackOfDiamonds

    JackOfDiamonds Advanced Corn Hole Diver

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    The Dunning–Kruger Effect springs to mind when reading this.

    Reminds me of the fine line between courage\competence and insanity, it is something i have witnessed many times in my life and the exact definition is always dictated by the outcome.

    If its insane but it works - he is competent.

    If it fails - he was insane and shouldn't have done that.
     
    eleniel, AfterDark, Dark Wolf and 2 others like this.
  3. jvogt

    jvogt ScubaBoard Sponsor ScubaBoard Sponsor

    # of Dives: 200 - 499
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    In hind site, I see the most dangerous part of yesterday's bike ride was nearly hitting a coiled rattle snake with my pedal. Looking down and seeing it coiled directly under my foot(wait, that's not a rock), I barely flinched as I peddled away. Survivor bias, or experience? Certainly not my first encounter with deadly snakes. Freaking out and loosing my balance while directly on top of the animal would have been very bad.
     
  4. JackOfDiamonds

    JackOfDiamonds Advanced Corn Hole Diver

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    I would call it luck more than anything.

    That snake on a different day may have chosen to strike before you would even notice it, or could be on a different day you could have been less aware of your surrounding and not move your leg in time to avoid being struck.
     
    Sam Miller III and AfterDark like this.
  5. chillyinCanada

    chillyinCanada ScubaBoard Supporter Staff Member ScubaBoard Supporter

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    Perhaps a bit of both, Jack?
     
  6. JackOfDiamonds

    JackOfDiamonds Advanced Corn Hole Diver

    # of Dives: I'm a Fish!
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    Could be, just my perspective of it.
     
    chillyinCanada likes this.
  7. lowwall

    lowwall Manta Ray

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    When I started diving, while I respected the water, I wasn't in the least worried about it. I was in very good physical shape and not that far removed from years of competitive swimming and water polo. I had also been a lifeguard and done a lot of body surfing and been a white water rafting guide, so knew I could remain calm when things went a little sideways.

    And then my wife decided she wanted to take OW so we could go on dive vacations together. She was a safe swimmer in a pool or calm ocean, but had no real athletic background and I was really worried about how she would handle stress underwater.

    So I decided to do some research on how safe or dangerous diving is for people like my wife doing the kind of tropical OW dives we were planning on doing together. I ended up finding the DAN Annual Reports. Reading through the fatality reports, you very quickly notice some common themes: diving in conditions well beyond the divers cert level (especially into overhead environments), diving with major known medical conditions, diving with known faulty equipment, diving with rebreathers, solo diving in difficult conditions.

    What you don't see in the fatality reports is healthy people doing open water dives, meaning non-obstructed surface and 130'/40m max depth. My conclusion was and is that SCUBA is actually extremely safe at this basic level.

    Edit: Taking the original analogy of mountain biking, this is riding on groomed beginner trails.
     
    waterone, eleniel, captain and 7 others like this.
  8. Bob DBF

    Bob DBF Solo Diver

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    Survivorship bias or survival bias is the logical error of concentrating on the people or things that made it past some selection process and overlooking those that did not, typically because of their lack of visibility. This can lead to false conclusions in several different ways. It is a form of selection bias.

    Survivorship bias can lead to overly optimistic beliefs because failures are ignored, such as when companies that no longer exist are excluded from analyses of financial performance. It can also lead to the false belief that the successes in a group have some special property, rather than just coincidence (correlation proves causality). For example, if three of the five students with the best college grades went to the same high school, that can lead one to believe that the high school must offer an excellent education. This could be true, but the question cannot be answered without looking at the grades of all the other students from that high school, not just the ones who "survived" the top-five selection process. Another example of a distinct mode of survivorship bias would be thinking that an incident was not as dangerous as it was because everyone you communicate with afterwards survived. Even if you knew that some people are dead, they wouldn't have their voice to add to the conversation, leading to bias in the conversation.


    In other words it's an issue if one only looks at a single example rather than the entire set. I was trained and make CSEAs successfully, my making the ascent successfully in itself may be survival bias, however when I started diving everyone was trained and used that procedure successfully so it was not survivor bias. Now, since rec divers aren't necessarily trained and do actual CSEAs, it may be that my experience will become survivor bias in rec diving.

    As far a SCUBA goes, there are few fatalities, the main cause being health related, and most causes being more conjecture than fact. This makes the choice between data and survivor bias hard to sort out.


    108' dive on an Al80 without redundancy, other than ones buddy, has been a particularlly usual occourance since the Al80 was produced, and with the old steel 72 before that. The stats say it is not survivors bias. Now I would say a bounce dive to 250' on an Al80 is survivors bias.
     
  9. Lorenzoid

    Lorenzoid idling in neutral buoyancy ScubaBoard Supporter

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    Survivor Bias, Dunning-Kruger Effect, Normalization of Deviance ... all relate to the same sort of thing.
     
    jadairiii and chillyinCanada like this.
  10. Bob DBF

    Bob DBF Solo Diver

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    Yes, I've seen all those phrases used as intellectual crutch to stifle a conversation instead of making a rational argument against a particular behavior. It seems some think it's the answer to the conversation rather than a concept that might be in play.
     
    dead dog, eleniel, Lorenzoid and 10 others like this.

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