This level is barely a fifth of the GDP per capita levels of more than $15,000 (at PPP) that existed in 1970 in developed economies in the region, when services contributed 50% of value added in GDP. Mandaluyong City, Philippines, ADB, 2013). For the stochastic frontier approach, see Denis J. Aigner, C.A. Knox Lovell and Peter Schmidt, “Formulation and estimation of stochastic frontier production function models", Journal of Econometrics, vol.