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On Wed, 2010-02-03 at 15:06 +0000, richard wrote: snip > for their justification of their method see ; > http://www.defra.gov.uk/esg/work_htm/publications/cs/farmstats_web/1_ABOUT_THE_SURVEY/FAQs_ABOUT_THE_DATA_AND_SURVEY/Introduction.htm#samplingstrategy > The sampling seems OK to me. Even though they "sample" all the biggies, they sample from all their strata and multiply up to estimate the contribution of all strata. The key para is Within each stratum holdings are sampled at random. The only exception to this is amongst the smallest holdings where a partially systematic approach is adopted to ensure that individual holdings are not usually sampled in successive years. This departure from randomness does create some risk of bias, but this risk is small, particularly since this stratum makes a relatively small contribution to the national totals for most crops. James > -- james kilty http://www.kilty.demon.co.uk -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html