Following the first positive score in four months, the Architecture Billings Index reversed direction in September. The ABI, an economic indicator of future building activity, reflects the approximate nine- to 12-month lag time between architecture billings and construction spending. The American Institute of Architects reported a September ABI score of 46.9, down from 51.4 in August. Any score above 50 indicates an increase in billings. The score reflects a sharp decrease in demand for design services, AIA said. The new projects inquiry index was 54.3, down from a reading of 56.9 the previous month. "It appears that the positive conditions seen last month were more of an aberration," said AIA Chief Economist Kermit Baker. "The economy is weak enough at present that design activity is bouncing around more than usual; one strong month can be followed by a weak one. The economy needs to be stronger to generate sustained growth in design activity." The index recorded the following regional averages: Midwest (51), Northeast (50.8), South (47.3) and West (46.7). Commercial/industrial was the strongest sector coming in at 52.4, followed by  mixed practice (50), institutional (48.0) and multifamily residential (46.4). The regional and sector categories are calculated as a three-month moving average, whereas the index and inquiries are monthly numbers. The ABI is sent to a panel of AIA member-owned firms. Participants are asked whether their billings increased, decreased or stayed the same in the month that just ended as compared to the prior month. Write to Kerry Curry. Follow her on Twitter @communicatorKLC.