Re: Uncertainty Question

[Peter Schoch <pschoch@NAC.NET>]

 From my mathematics coleagues and my study of statstics in this area, I
have a few questions:

1.  How did you arrive at the +/-0.03?
2.  Is this the estimated accuracy?
3.  Is this derived from the sample standard deviation?
4.  Or, is the standard error?

How you report the next step depends upon which of these you are using.
I prefer to use standard error.  Once you compute that value, it is
generally accepted that the first ignificant digit in the standard error
is the last significant digit in the average.  It also seems to always
work out that this gives the correct number of significant figures.

Peter Schoch
Sussex County Community College
pschoch@nac.net

Ken Fox wrote:
> I admit it, as part of my required curriculum I have to teach more about
> uncetainties than I am confident about. The rules are inconsistent from
> text to text and common sense does not always prevail. Is there a simple
> guide book?
>
> Here is my current question:
> Measuring the density of a 3x5 card as an exercise in sig.fig.s and
> uncertainty. Some groups used a micrometer to measure the thickness,
> others made a stack of 50 and measured the group with a cm ruler. This
> group measured the stack as 1.23 cm =/- .03 cm. We divide by 50 for the
> stack. How do YOU report the uncertainty?
>
> Ken Fox
> Smoky Hill High School
> 16100 Smoky Hill Rd
> Aurora,CO 80015
> 303-693-1700(w)
> 303-850-7537(H)
> kfox@stega.smoky.org