"In 2002, California experienced its highest out-migration in seven years — 52.1 percent — according to United Van Lines' study of the company's 198,571 interstate household moves in the 48 contiguous U.S. states and Washington D.C."
The article also has a few other indirect measures of the difference between the numbers moving into CA and those moving out. For example:
"Renting a 17-foot U-Haul truck for a one-way trip from Flagstaff, Ariz. to San Jose at the end of February is $377, according to the company Web site. Reversing the trek, however, is a whole different story. It's $843 to rent the same truck in San Jose and drive it out of town to Flagstaff on the same day. The same kind of price differential is true at Budget where leaving Flagstaff for San Jose on Feb. 28 in a 15-foot truck costs $211.50, and flipping the trip costs $1,074.60."
Hope this was helpful.