Editor’s note:  Construction Citizen is proud to partner with AGC America to bring you AGC Chief Economist Ken Simonson's Data DIGest. Check back each week to get Ken's expert analysis of what's happening in our industry.Construction spending hits four-year high; AGC survey finds challenges filling positionsCheck out Ken Simonson's upcoming speaking schedule.Construction spending in July reached a four-year high of $901 billion at a seasonally adjusted annual rate, up 0.6% from June and up 5.2% from July 2012, the Census Bureau reported on Tuesday.  Census revised up the totals for June and May by $12 billion and $7 billion, respectively, which may lead to an upward revision in the second-quarter estimate for growth in gross domestic product (GDP) later this month.  Private residential spending increased 0.6% for the month and 17% year-over-year.  Private nonresidential spending rose 1.3% and 2.0%, respectively.  Public construction spending fell 0.3% and 3.7%.  Of the three residential components, new single-family construction grew 0.5% and 29%; new multifamily spending, 0.1% and 39%; and improvements to existing single- and multifamily buildings, 0.8% and 1.4%.  The three largest private nonresidential components (in descending order of current size) all increased from one and 12 months ago: power construction (including conventional and renewable power plus oil and gas fields and pipelines) 0.5% and 5.0%, respectively; manufacturing construction 2.9% and 0.8%; and commercial (new and renovated retail, warehouse and farm), 1.7% and 2.6%.