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Re: (meteorobs) Doomsday Icarus
Malcolm reminded me of what I should have known thusly :-)
>There are two points here.
>1) +/- is one standard deviation, i.e. approximately 68 per cent of
>the time the value will lie between +210,000 and -150,000. It does
>not mean that the value only lies between these two values. The
>probability drops off as you move away from the estimated perigee. A
>perigee of 600,000 is only a three-standard-deviation event. So it is
>possible, albeit unlikely at somewhat less than 1 per cent.
While this should have been obvious to all of us (If I was awake that
is :->), I am 90% (+/- 30%) sure that the vast public audience has no
concept of statistics, hence without an explanation, the error bars are
meaningless to most people who will be getting the story from "the media".
Perhaps this thought should be raised to Brian Marsden for the next time
such a press release is needed.
>2) There are formal/internal and systematic/external errors. Given
>the original data, the formal/internal error budget based upon the
>data then to hand was +/- 180,000. However, as is usually the case,
>the systematic errors (because the data are insufficient or biased, or
>you make invalid assumptions) are often much larger. A classic case
>is the determination of the Hubble parameter. Sandage would quote a
>formal error of say 50+/-2 km/s/Mpc, but given other results, the true
>error is much larger because of systematic uncertainties and biases.
An excellent example here for the scientific audience. I again suggest the
public would see the ongoing refinement of the hubble constant (and by
extension, the age of the universe, ages of stars problem) as scientists
not knowing what they are talking about.
>Malcolm
Thanx Malcolm, I've turned on the rest of my brain now :->
Wayne