Confidence intervals are indicators of the extent to which the estimate may differ from the true population value. The larger the confidence interval, the less precise is the estimate.
The 2011 Census estimate for the England and Wales population had a 95 per cent confidence interval width of plus or minus 0.15 per cent (plus or minus 83,000 people).
Census estimates used the Census Coverage Survey to measure coverage of the census and to provide estimates of the population, including people missed by the census. A basic requirement of any estimate is a measure of its precision or uncertainty. A 95 per cent confidence interval, which provides a measure of accuracy, can be interpreted as the interval within which 95 times out of 100 the true value will lie if the sample were repeated 100 times.
Download the spreadsheet for confidence intervals calculated for the age-sex estimates down to local authority level. Download the paper for an outline of the method used.