Jonathan Rothwell, Brookings: “This report uses a unique database from the labor market information company Burning Glass and other sources to analyze the skill requirements and the advertisement duration time for millions of job openings. It reaches the following conclusions:

• Job openings for STEM positions take longer to fill than openings in other fields. 
  The median duration of advertising for a STEM vacancy is more than twice as long as for a non-STEM vacancy. For STEM openings requiring a Ph.D. or other professional degree, advertisements last an average of 50 days, compared to 33 days for all non-STEM vacancies.
• Specific high-value skills requested by employers and common to STEM occupations are particularly scarce relative to demand and yet particularly valuable to employers.
• The regional supply of workers in a given occupation affects the length of vacancy advertisements. 
  The typical job opening in an occupation for which the regional unemployment rate was below 3 percent was advertised for 16 days; most of these occupations are in STEM fields. By contrast, the typical job opening was advertised less than half that duration (seven days) for occupations with regional unemployment rates above 10 percent.“