In today’s article about the ubiquitous “unexpectedly” adverb in economic reports, I note that President Obama likes to talk about how many consecutive months the American economy has seen private-sector job growth.

What Obama says is technically true — I suppose Vice President Biden would say “literally” — but increasing the number of private-sector jobs doesn’t necessarily bring down the unemployment rate. The single biggest factor is that the size of the labor pool normally grows from month to month, and while economists disagree on precisely how many jobs need to be added each month just to keep pace with the additional workers, it generally ranges from 100,000 per month (AP) to 100,000 to 125,000 (Heritage Foundation) to about 130,000 (New York Times). Some say a “sustained recovery” requires 250,000 jobs per month.

For perspective, the U.S. economy lost 8.8 million jobs in this recession.

All figures are from the Bureau of Labor Statistics.

Private-Sector Job Growth, by Month July 2011 154,000 (preliminary) June 2011 80,000 (preliminary) May 2011 99,000 April 2011 241,000 March 2011 219,000 February 2011 261,000 January 2011 94,000 December 2010 167,000 November 2010 128,000 October 2010 193,000 September 2010 112,000 August 2010 143,000 July 2010 117,000 June 2010 61,000 May 2010 51,000 April 2010 241,000 March 2010 158,000 February 2010 62,000 January 2010 16,000 December 2009 -83,000

Depending on your measuring stick, during these 19 months of private-sector job creation, the U.S. only “gained ground” in 12 of them (if the threshold is 100,000) or 9 of them (if the threshold is 130,000). At no point has job creation hit the “sustained recovery” threshold.

One last point: In April 2010, Vice President Biden declared, “I’m here to tell you, some time in the next couple of months, we’re going to be creating between 250,000 jobs a month and 500,000 jobs a month.”