A major methodological change introduced for the new survey in 2000 was the introduction of weighting and grossing. A full description of this can be found in the 2000 report with additional technical papers on the website.

A dual weighting scheme was introduced. First, weighting to compensate for non-response in the sample based on known under-coverage in the Census-linked study of non-response (Foster, 1994). Second, the (weighted) sample has been weighted (grossed) up to match known population distributions (as used in the Labour Force Survey). The substantive chapters of the report present data for 2001/2 in weighted form only. For further details of the weighting see Appendix D. Details of presentation of the data in report tables can be found in ‘Notes to tables’.

The results from the 2001 Census, published on 30 September 2002, showed that previous estimates of the total UK population were around one million too high, with disparities being most apparent among men aged 25 to 39. These disparities were larger than expected and thus have two implications for figures presented in this report:

• some of the percentages may need revision as they are based on old population figures
• the weighted bases will all change to some degree because of the reduction in estimated population size.

Thus, for this 2001 report the general caution regarding the use of weighted bases is re-iterated. Weighted bases should primarily be considered as bases for the percentages shown rather than estimates of population size.

Revised GHS data will be released in Spring 2003, focussing on results where percentage estimates have been affected. For more details about the revised census-based estimates see www.statistics.gov.uk/census2001.