T he overall aim of the NHS R&D Health Technology Assessment (HTA) programme is to ensure that high-quality research information on the costs, effectiveness and broader impact of health technologies is produced in the most efficient way for those who use, manage and work in the NHS. Research is undertaken in those areas where the evidence will lead to the greatest benefits to patients, either through improved patient outcomes or the most efficient use of NHS resources. The Standing Group on Health Technology advises on national priorities for health technology assessment. Six advisory panels assist the Standing Group in identifying and prioritising projects. These priorities are then considered by the HTA Commissioning Board supported by the National Coordinating Centre for HTA (NCCHTA). This report is one of a series covering acute care, diagnostics and imaging, methodology, pharmaceuticals, population screening, and primary and community care. It was identified as a priority by the Methodology Panel and funded as project number 93/50/04. The views expressed in this publication are those of the authors and not necessarily those of the Standing Group, the Commissioning Board, the Panel members or the Department of Health. The editors wish to emphasise that funding and publication of this research by the NHS should not be taken as implicit support for the recommendations for policy contained herein. In particular, policy options in the area of screening will be considered by the National Screening Committee. This Committee, chaired by the Chief Medical Officer, will take into account the views expressed here, further available evidence and other relevant considerations. Reviews in Health Technology Assessment are termed 'systematic' when the account of the search, appraisal and synthesis methods (to minimise biases and random errors) would, in theory, permit the replication of the review by others.

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Southeastern Australian populations of the dioecious, subtidal sea anemone Anthothoe albocincta display considerable spatial variation in the colour patterns of the constituent polyps, and the most visually striking feature of local populations are sets of dense aggregations each comprised of polyps with a single colour pattern. We used a combination of genetic data, observations and manipulative experiments to infer that A. albocincta generates these monomorphic aggregations via asexual reproduction and that asexual reproduction plays the major role in the maintenance of established population~. Allozyme electrophoresis of 2 to 5 polyps from each of 20 mapped aggregations (in 2 populat i o n~) revealed that in 18 cases (9OU4~) all polyps were electrophoretically identical and always distinct from differently coloured polyps tdken from each of 26 adjacent aggregations. Furthermore, the genetlc structure of each of 13 populations separated by u p to 930 km was consistent with the predicted effects of localised asexual recruitment. We detected 16 heterozygote excesses and 11 heterozygote def~cits ( p < 0.05) in a total of 66 tests for departures from Hardy-Weinberg equilibria. Moreover, each population contained significantly less [p < 0.005) multi-locus genotypic diversity (G,) than was expected for a randomly mating population (G,) (mean Go:G, = 0.30) and contained relatively few unique 7-locus genotypes. Some genotypes were found within many aggregations, suggesting successful clones may have extensive a n d discontinuous distributions within populations. In addition, we observed longitudinal fission of adult polyps in both field and laboratory conditions, and found that over a 6 mo period 82% (i.e. 1469 of 1790) of new recruits into 30 experimentally cleared patches, within 3 populations. were morphologically identical to those within surrounding aggregations. These data, together with our earlier analysis of genetic variation among populations, and observations of gonad development, imply that this specles uses fission to maintain populations, consisting predominantly of spatially restricted clones (each with an almost unique colour pattern), but uses sexual reproduction to produce widely dispersed colonists.

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