Another day, another study with another indicator showing how the economy appears to be humming along.

On Wednesday, the American Institute of Architects released June's Architecture Billings Index, which is called a "leading economic indicator of construction activity."

The index, which reflects the nine- to 12-month lead time between architecture billings and construction spending, was 53.5 for the month, up from 52.6 in May.

AIA says the score reflects an increase in design activity — and any score over 50 means there's been an increase in billings. Two other measures, New Projects Inquiries and New Design Contracts, increased to 66.4 and 55.7, respectively.

The score for design contracts in June was the highest mark since the tally began in ­October 2010.

The data "is indicative of a sustainable strengthening across the construction marketplace," said Kermit Baker, AIA chief economist. "With the first positive reading since last summer in billings at institutional firms, it appears that design activity for all major segments of the building industry is growing. The challenge now for architecture firms seems to be finding the right balance for staffing needs to meet increasing demand."

A few more highlights: The Midwest was the highest-scoring region of the country in overall billings at 56.3. By sector, multifamily residential was 57.7, mixed practice was 53.8, commercial/industrial was 53.1 and institutional, 50.2.