Investors appear optimistic about the U.S. labor market ahead of March employment figures scheduled for release today. Shares of staffing-related companies jumped 9.7 percent in March, the biggest gain since 2013. The Standard & Poor’s Supercomposite Human Resources & Employment ServicesIndex, composed of Robert Half International Inc., ManpowerGroup Inc. and eight others, leads its benchmark gauge by 6.7 percentage points since the measure hit a low in February. While these companies benefit largely from demand for temporary workers, their stock performance is influenced by total job gains. Economists surveyed by Bloomberg estimate U.S. employers added205,000 workers in March, compared with 242,000 the previous month.