When an estimator is defined under this sampling design, its variance and bias remain the same over survey months, but it is not so under other existing rotation designs.
For the one-tail sampling scheme, we selected 1,000 trios from the 5,000 (i.e. the top 20%), as convergence problems were encountered when using only 500 trios under this sampling scheme.
Under this sampling design, differences in P between central and marginal populations compared to those seen between the populations of their paired species can be interpreted as indicative of processes operating in geographically marginal populations.
Also while the male population was under-represented in this sample, the gender sub-samples met the statistical size requirements.
Future work could try to include more non-white and male professionals, who were under-represented in this sample.
Males, individuals from Black and minority ethnic groups and those with a diagnosis of schizophrenia/schizoaffective disorders were under-represented in this sample.
However, women under 24 years of age and those living outside of urban areas appeared slightly under-represented in this sample which may limit the generalisability of the findings to these women.
When compared with national statistics for GPs [ 16], female GPs, as expected, were significantly under-represented in this sample (18% vs 36%), as were non-partner GPs (6% vs 15%).
Individuals in the lowest employment grade also were under-represented in this sample, comprising only 11% in the cross-sectional analysis group, and only 9% in the prospective analysis group, with the remainder split approximately equally between the two higher employment grades.
Under the microbeam, this sample showed strongly varying behavior from place to place.
