Re: ID cards - What wasn't mentioned about the results of the consultation exercise

[Andrew McLean <[EMAIL PROTECTED]>]

In message <[EMAIL PROTECTED]>, Roland 
Perry <[EMAIL PROTECTED]> writes
> The American pollsters on TV this morning are saying that a *carefully 
> selected* representative sample of 1000 voters [asked one question] 
> will result in a +/- 3% accuracy. As one of then said "if the result 
> appears to say Bush will win by 2%, then problems with the sample could 
> mean that actually Kerry might win by 1%".
>
> They then said that to get 1% accuracy you'd need a sample of 3,000, 
> which is suspiciously linear, and therefore I doubt it.

You are right to doubt it. Assuming the sample is a small fraction of 
the total population, then the error due to sampling effects is, to a 
good approximation, inversely proportional to the *square root* of the 
sample size. Of course, this error estimate is an underestimate, as it 
completely ignores the systematic effects due to not having a 
representative sample.

--
Andrew McLean