Re: OT: definition of "significant figures"

["Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk>]

On Fri, 29 Jul 2005 16:46:36 +0200, Jacob Sparre Andersen wrote:

> tmoran@acm.org writes:
> 
>> Given a set of measurements x(i), I'd like to print their average to
>> the "correct" number of significant figures.  eg
>>   1.11, 1.12, 1.08 => "1.1",   1.11, 1.25, 1.35 => "1"
>> I've got some adhocery that more or less does it, but is there a
>> moderately standard, formal, definition?
> 
> The base 10 logarithm of the standard-deviation of your measurements.

this looks like one of those physicist's sign errors!

How about:

*Minus* the base 10 logarithms of the standard deviation =>
  *decimal places*

For example:
SD=0.1   => use 1 decimal place
SD=0.001 => use 3 decimal places

Note that decimal places are not significant figures!

Significant figures = Log10 (mean / standard deviation) + C

I think people also add in the (small) constant, for
good measure, depending on how they feel about the data distribution.

YMMV
-- 
Adrian