ByJohn S. McClenahen The Conference Board's leading economic index for Mexico increased 0.6% in August, the most recent month for which data are available. The index now stands at 145.0 (1990=100). The August increase matches the 0.6% rise recorded in June and is six times the 0.1% July increase. But not all the data are that encouraging. "Despite [August's] increase, the growth rate of the leading index has continued to slow from its peak earlier this year, and its strength has become somewhat less widespread," says the Conference Board, a New York-based business research group.