The Architectural Billings Index ("ABI") is a diffusion index that tracks growth in billings for design work at architectural firms from month to month across the United States. It is computed from survey responses from thousands of architectural firms throughout the U.S. who are asked to report if billings went up or down compared to the prior month. A value above 50 shows growth in billings, while any value beneath 50 indicates shrinkage. Any growth or contraction in billings will naturally lead to corresponding construction spending or lack thereof, as the buildings designed by architects