> Confused enough now? :)
Jay Warner writes as if confidence intervals relate to the means on
population. But what of the use of confidence intervals relating to the
estimates of population?
According to the UK Census (conducted in 1991) the population was 58,789,194
persons. In releasing this figure the Office for National Statistics
declares that:
'Because the final numbers are estimates, error levels can be used as a
guide to accuracy. For England and Wales, the confidence interval -
reflecting error levels arising for a number of reasons - on the whole
population is +/-0.2 per cent, or a total of 104,000.
The estimates of under-enumeration, and thus the census results, are based
upon a sample survey, the Census Coverage Survey (CCS) and are therefore
subject to sampling error. This is an important difference with previous
census results, as the final numbers are all estimates rather than a simple
count, and the error levels can be used as a guide for assessing the
accuracy of the estimates. Standard statistical techniques have been used to
calculate these error levels, and therefore produce confidence intervals for
the One Number Census (ONC) results.' (see
http://www.statistics.gov.uk/census2001/default.asp)
Are these really 'standard statistical techniques' ?
And, maybe a different question, is the concept of confidence level
applicable where the main sources of error are likely to be non-sampling
errors?
Ray Thomas, Social Sciences, Open University
Tel: 01908 679081 Fax 01908 550401
Email: [log in to unmask]
35 Passmore, Milton Keynes MK6 3DY
**************************************
> -----Original Message-----
> From: Jay Warner [mailto:[log in to unmask]]
> Sent: 10 October 2002 20:18
> To: [log in to unmask]
> Subject: Re: FW: RE: QUERY - SPSS (try 2)
>
>
> the std error, or the estimated std error, can estimate the variation
> expected in a measured _average_ of a sample. We call this
> 'variation' the confidence interval. We can also use this confidence
> interval to predict the location of the true mean of the population,
> using the same confidence interval and the measured average
> of the sample.
>
> Thus, some people refer to the estimated standard deviation as the
> standard deviation of a single measurement (the next one), and refer
> to the standard error as the standard deviation of the average. While
> the two terms perform the same assessment for the respective point
> measurements, the terminology has just gotten quite
> confusing. True?
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