The expert fact-checkers/liberal bloggers at PolitiFact show everyone how to figure out whether legislation kills jobs.
PolitiFact uses two methods. The first method shows whether the Affordable Care Act caused job loss. The second method shows whether the North American Free Trade Agreement caused job loss.
Here's PolitiFact's method for the ACA, from a fact check of Sen. Ted Cruz (R-Texas, bold emphasis added):
Cruz said that Obamacare cost the country millions of jobs and had forced millions into working part-time.PolitiFact apparently reasons that if that overall employment numbers improved then it doesn't count toward Cruz's point that "The law might have affected part-time work for certain kinds of people."
The government’s employment surveys show no sign of that occurring. By every measure, millions more people are working and millions fewer are stuck unwillingly in part-time work since the time the Affordable Care Act became law. The law might have affected part-time work for certain kinds of people, but that didn’t change the improvement in the overall numbers.
Here's PolitiFact's method for NAFTA, as related in a fact check of Sen. Bernie Sanders (I-Vt.):
Sanders said that NAFTA, which Clinton used to support, cost the U.S. economy 800,000 jobs. There is a report from a left-leaning policy group that reached that conclusion. On the other hand, many other nonpartisan reports found that the trade deal produced neither significant job losses nor job gains. This is a result of competing economic models and the challenges of teasing out the effects of NAFTA from everything else that has taken place in the economy.The biggest difference between the two methods comes from PolitiFact's reliance on raw employment numbers when checking the claim from Cruz. Raw employment numbers were a non-factor in checking Sanders but the key to giving a "Pants on Fire" rating to Cruz.
The report Sanders cited is an outlier, and his use of its findings ignores important facts that would give a different impression. We rate his statement Mostly False.
PolitiFact cited studies supporting and contradicting Sanders, but gave no evidence supporting Cruz. The fact check of Cruz omitted mention of a Congressional Budget Office report estimating supply-side net reductions in labor (workers deciding not to work or to work fewer hours), the equivalent of about 700,000 full-time jobs.
We reason that since PolitiFact is objective and non-partisan, it follows that only a non-objective and non-non-partisan (okay, partisan!) source would mention the findings of the CBO relating to unusually slow job recovery following the 2008 recession. In the world of PolitiFact, supply-side job loss doesn't count and doesn't even apparently affect the economy.
Or, to borrow a bit from Stephen Colbert, the fact[checker]s have a liberal bias.
Jeff Adds: Note that Jon Greenberg wrote both the NAFTA and ACA pieces. This makes it even more difficult to reconcile the use of two different methods in performing the fact checks.
Correction March 10, 2016 (bww): I inexplicably identified Delaware as the state Bernie Sanders represents. The text has been changed to identify Vermont as the state Sanders represents in the Senate.