How things have changed! In 1995 the United States can look back on five years of solid growth while Japan has been struggling.Few Americans attribute this solely to such obvious causes as a devalued dollar or the turning of the business cycle.Self-doubt has yielded to blind pride.'American industry has changed its structure, has gone on a diet, has learnt to be more quick-witted,' according to Richard Cavanagh, executive dean of Harvards Kennedy School of Management.'It makes me proud to be an American just to see how our businesses are improving their productivity,' says Stephen Moore of the Cato Institute,a think-tank in Washington.