See these reports and studies.
Task Force on New Americans Report
USCIS Office of Fraud Detection and National Security - USCIS Form I-90 Benefit Fraud Assessment Summary
Employment Eligibility Verification Evaluation Reports
E-Verify Customer Satisfaction Survey, October 15, 2010
Office of Policy and Strategy Reports
USCIS Program Reports: H-1B & H-2B
USCIS Program Reports: EB-5