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    Re: What precision is required in cel nav?
    From: Lu Abel
    Date: 2015 Jul 19, 19:41 +0000
    Francis:

    At the risk of starting an argument that will soon outdistance my knowledge of statistics, I think there is a difference between drawing conclusions from a set of data (eg, the effectiveness or side effects of a drug) where you know nothing ahead of time about its statistics, and drawing conclusions from a set of data where you know what it should look like. 

    Say, for example, I take a set of sights.  I can say with confidence that they ought to be going up (body ascending), going down (body descending) or be roughly the same (body at meridian transit). 

    Given that I am taking imprecise measurements of precise phenomena (the position of a body in the sky) it is quite reasonable to question the accuracy of a shot if it is a severe outlier from the expected results.   ("Shooting the dissident" was the way my statistics prof termed it)

    Lu


    From: Francis Upchurch <NoReply_Upchurch@navlist.net>
    To: luabel@ymail.com
    Sent: Sunday, July 19, 2015 12:11 PM
    Subject: [NavList] Re: What precision is required in cel nav?

    Umh!
    John, re the stats
    I'm certainly no mathematician, but statistics I do know.(medical research).
    There are lots of problems with this. Very selective data ("cherry picking", we call it ) and fairly arbitary exclusion of "bad outliers" . This would never get past the FDA I can tell you that from 30 years experience. I very much doubt these data are worth the paper they are written on.
    Perhaps a professional statistician could give their opinion?
    Also, I assume all done on big ships? Not 30-40ft yachts? Umh.
    I personally do not believe a word of this. But happy to be corrected by those who know better!
    Best wishes
    Francis


     


       
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