In the last issue of Houston Business , we introduced a new coincident index of economic activity for Houston based on employment, the unemployment rate, real wages and real retail sales. The index optimally weights and combines the data to best portray the Houston economy. It is most useful as a tool to gauge current economic conditions. The index shows Houston slogging through a mild but prolonged decline. Economic activity peaked in April 2001, followed first by a decline of less than 1 percent and then by a long period of no growth that extends to the present.