Outside hires typically take twice as long to reach full productivity as in-house hires, according to a study by Mellon's Human Resources & Investor Solutions Service. The study says executives hired from the outside typically take 26 weeks to complete learning curves, compared to 16 weeks for inside hires. For managers, the figures average 25 weeks for external hires and 14 weeks for internal ones. For clerical workers, the averages are 20 weeks versus eight weeks. Internal hires exhibit 50 percent fewer unproductive days during their learning periods. Lesson: Encourage managers to consider internal candidates first.