The validity of using Countryside Survey sample data from Great Britain to estimate land cover in Scotland

It is possible to make environmental or ecological descriptions of geographical regions using data not only collected within the region concerned but also from a wider area. Producing accurate descriptions of a region using broader datasets is financially appealing as it should reduce the intensity and hence the costs of regional survey. However, it is essential that any information collected outside the region is only ever used to describe similar situations and conditions within the region. An appropriate stratification may offer sufficient structure within a dataset to identify which parts to include and which to exclude, but, if not used carefully, it can produce inaccurate results. This problem is explored using the Institute of Terrestrial Ecology (ITE) Land Classification, a sampling stratification used to structure ecological and environmental surveys in Great Britain (GB). Using this stratification, national and regional estimates of land cover and estimates of the extent of rural features in England, Scotland and Wales have been produced by ITE from sample surveys undertaken in 1978, 1984 and 1990. The published estimates for Scotland, for example, make use of the complete GB sample dataset for land classes occurring in that region. The work described here shows that the Land Classification offers a legitimate stratification scheme for sampling Scotland, setting it in the context of GB. Overall, it suggests that, in most cases, it is preferable to make national estimates for Scotland from the full GB sample. The consequences of restricting the sample set to those samples drawn only from Scotland is to reduce the sample size and subsequently statistical confidence in the result. The implications of these findings for other studies are examined