Unfortunately there are no other surveys this specific (to Cisco certifications) and so, good or bad, these are the only income stats available. If anything is skewed in terms of income levels it was done so by the hundreds of certified professionals completing a global survey (maybe only those with higher paying jobs chose to complete it?). The long-term growth % is what the U.S. government is currently projecting (and that number came out within the last few months)...