There are eleven such clusters, but they can also be organised, by grouping 10 of them into pairs, into an alternative structure of six clusters. The cluster totals are presented on Sheet 1 of each table. The proportions of men and women of different age groups among those responding in each Authority were not identical. The weights for the totals shown on Sheet 1 of each table have been adjusted to take account of the varying sample fractions necessarily employed in each HA to generate a selected sample of 1000 in each one. Each of 6 and each of 11 clusters has also been age and sex standardised to mid-1997 national estimates.
All survey data are estimates of the true proportion in the population sampled.
With random sampling methods it is possible to estimate the margins of error either side of each percentage indicating a range within which the true percentage will fall. These margins of error vary according to both the percentage estimates from the sample, and the number of people included in the sample. Tables 14 and 15 present the answers to questions which applied to relatively few respondents. Quality and performance in the new NHS .