What is the size of the total contingency recruiting market in the
United States, in terms of total revenue?  How fast is it growing (or
declining)?  How is the market broken down by industry segment (e.g.,
healthcare, finance, technology, etc.)

Note: I am looking for figures for the "CONTINGENCY recruiting" market
only (also called contingency staffing or headhunting), but NOT
"RETAINED recruiting".  Thank you