>> I may not be the only one confused on what these confidence intervals
>> mean. In the above press release, the Gallup organization provides this
>> description of what their +/- 2% means:
>>
>> "For results based on the total sample of likely voters, one can say
>> with 95% confidence that the margin of sampling error is +/- 2
>> percentage points."
>
>Those guys are supposed to be professionals, and they should have
>been polishing their syntax for 50 years, but my first reaction to
>that statement was "UGH."
Indeed. Of course, they don't mean that there's any uncertainty as to
what the level of uncertainty is - that's just their terrible syntax.
More seriously, the statement is false. The intended audience for
this statement will read it as meaning that there is a 95% PROBABILITY
that the true value is within 2% of the stated value, which is of
course not correct. Only (some) statisticians have mangled the
definition of the word "confidence" in such a way as to make this a
true statement.
The standard wording in Canada seems to be
The results are correct within 2 percentage points, 19 times out of 20.
which has the virtue of being true, although I'm not sure many readers
really grasp it's implications.
----------------------------------------------------------------------------
Radford M. Neal [EMAIL PROTECTED]
Dept. of Statistics and Dept. of Computer Science [EMAIL PROTECTED]
University of Toronto http://www.cs.utoronto.ca/~radford
----------------------------------------------------------------------------
=================================================================
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
http://jse.stat.ncsu.edu/
=================================================================
