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Estimating the FUTURE!

  1. Nov 20, 2008 #1
    Suppose I have a radar gun that can measure velocity with an internal error with a mean of 3 m/s and a standard deviation of 1m/s on that error
    eg velocity
    10 +- 2.8
    6 +- 3.1
    21 +- 3.2

    and so on. Now I want to make a prediction of the future when I get a new radar gun. It will have an internal error of roughly 1m/s
    How then do I scale the std deviation? by a factor of three?
    Thanks all!
    Last edited: Nov 20, 2008
  2. jcsd
  3. Nov 20, 2008 #2
    A change in the mean doesn't have to change the standard deviation.
    The standard deviation could still be 1m/s.

    For example {3,4,5,3,4,5} and {7,8,9,7,8,9} have the same standard deviation but different means.

    You really need more data to establish a future variance and standard deviation.
  4. Nov 20, 2008 #3
    If you were to make an educated guess would it make sense to scale the std?
    What other data would you need?
  5. Nov 20, 2008 #4
    No, not without more information.

    You need to know if the variance has changed.

    If your future radar gun is no more precise, but simply more accurately calibrated, your average will change but the variance and std.dev. will not.
  6. Dec 2, 2008 #5
    I would think that math could explain & tell every little detail about the future, however I think that you would have to have an equation for everything, so until this "Quantum Theory" stuff is solved. Until then, I think all you 'can' do is make an educated guess. : )
    Last edited: Dec 2, 2008
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