NAFTA: No Statistically Significant Effect on Jobs
Actually, using these payroll data from the BLS (via FRED), the percentage increase from January 1980 (90,800,000) to December 1993 (112,206,000) is 23.57%, and the percentage increase from January 1994 (112,474,000) to December 2007 (138,119,000) is 22.80%, and not 13%! In other words, on a percent change basis, job growth in the 14-year period before NAFTA was almost exactly the same as the 14-year period after NAFTA.
For a more sophisticated statistical analysis, see the chart above with results of a difference-in-means t-test of the null hypothesis that there is no difference in monthly job growth in the pre-NAFTA and post-NAFTA periods. The results suggest that there is no statistical difference in job growth during the 1980-1993 period and the 1994-2007 period. Further, especially for payroll employment, the variability of monthly job growth (measured by the standard deviation) was much lower post-NAFTA (.1300%) than pre-NAFTA (.2152%), suggesting much greater stability in job growth after NAFTA.
Bottom Line: NAFTA had no statistically significant effect on U.S. job growth.