The plunging financial markets this month, followed by unprecedented responses from the federal government, have left many Americans bracing for a deep recession. In the architecture profession, however, the downturn has already arrived, according to a key measure of the market for architectural services.

As of August, the Architecture Billings Index (ABI), which the American Institute of Architects compiles in part from statistics provided by firms, had dipped below 50 for seven straight months, hitting 39.7 in March, the lowest score in the index’s 13-year history. Anything below 50 represents a billings decrease. In contrast, the score rose above 50 every month last year; in fact, prior to 2008, the score had dropped below 50 on only one occasion (June 2006) in the past three years.