LONDON - The Anglo-Dutch media group has announced a £570 million ($993m; €832m) share buyback scheme over the next three years in a bid to boost investor confidence.    Reed-Elsevier, which publishes The Lancet medical magazine and owns the LexisNexis legal service, has reported full-year results at the lower end of analysts' expectations as turnover in 2005 rose 7% to £5.2bn, while pre-tax profits rose from £631 million to £701m.