> OK here is the lowdown. These were 200 tests of how accurately I could
> juggle two sharp knives and a bottle of nitroglycerine. Each miss
> represents one trip to the hospital. ;-)
>
> Actually (seriously) the tests are of two barcode scanners. Each group of
> ten was ten consecutive scans of the same product. In a successful test
> the scanner read the UPC code in one pass. Some packages have different
> color ink, wrinkly bags, shiny surfaces, others are flat black ink on
> cardboard boxes. So yes, the sets of ten are *different* but the idea is
> to get an overall mix of products that might represent a shopping basket
> full.
>
> Of course, the consequences of a miss are not catastrophic, just annoying.
> And there is another annoying thing, some products will not scan at all
> with either scanner.
>
> I guess my statistics question is this: Given that the standard deviation
> of the data is over 30%, is a difference of 9% between one scanner and
> the other *signifigant*? Or is this fact even relevant?
>
> -- Lawrence Lile
>
>
>
>
>
>
> Wagner Lipnharski <
@spam@wagnerKILLspamUSTR.NET>
> Sent by: pic microcontroller discussion list <
KILLspamPICLISTKILLspamMITVMA.MIT.EDU>
> 04/17/2003 01:07 PM
> Please respond to pic microcontroller discussion list
>
>
> To:
RemoveMEPICLISTTakeThisOuTMITVMA.MIT.EDU
> cc:
> Subject: Re: Fun with Statistics - Which is better?
>
>
> Lawrence Lile wrote:
> > Which unit is better?
> >
> > I have two units, one is supposed to be "improved" over the other. I
> > ran 200 tests on each unit, and recorded the number of successful
> > tests out of each group of ten tests. I am trying to prove to
> > myself whether one is actually better than the other, or that the
> > differences are insignifigant, statistically. Here is the raw data
> >
> > Successful tests
> > out of ten tries
> >
> > unit1 unit2
> > 10 10
> > 3 2
> > 5 10
> > 10 9
> > 10 6
> > 0 0
> > 7 9
> > 10 10
> > 8 8
> > 0 5
> > 7 6
> > 2 6
> > 9 8
> > 7 10
> > 8 9
> > 10 10
> > 4 10
> > 0 1
> > 3 3
> >
> > 113 132 out of 200 total # tests
> > 57% 66% success rate
> >
> > Avg 5.947368421 6.947368421 Average
> > St. Dev 3.703957106 3.341218743 St Dev
> >
> > Now on the surface Unit 2 looks slightly better than unit 1.
> > However, the standard deviations are so large, maybe it is just a
> > statistical fluke and next time unit 1 will look better. Any body
> > got enough math whizzing around their brain to tell?
> >
> > P.S. THe manufacturer says the tests should be 95% successful. Yeah
> > right.
> >
> > --Lawrence the Skeptical
>
>
> All will depend on the kind of test.
> If the group of 10 tests are exactly the same, then it is not 20 tests of
> 10, it was simply 200 tests, and the result is 113 x 132.
>
> Statistics are very tricky. Suppose the lotto number 35 was not drawn a
> single time during the last 52 Saturdays, what are the chances of the ball
> #35 to be drawn next Saturday? Exactly the same as any other ball...
> since
> the past results does not interfere in the next draw, everytime happens to
> be a fresh brand new opportunity to all the numbers. Except of course if
> the ball #35 is heavier, lighter, bigger, smaller, etc, what is not the
> case, since they always replace the whole set of balls every Saturday for
> new ones never used, exactly to avoid this kind of crazy thoughts.
>
> If your result is basically 113 x 132, there is no tricky stat wizard that
> will convince you otherwise, but in your place, I would love to see the
> explanation why the Unit#2 made 10 in the first and third, and only 2 in
> the second group of tests... that would be an interesting explanation...
>
> Wagner.
>
> --
>
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