Keerativibool, W. “Costs and Benefits Gained from Planting Para Rubber in the form of System of Simultaneous Equations: A Case Study of Pa Phayom District, Phatthalung Province and Thung Song District, Nakhon Si Thammarat Province”. NIDA Development Journal, vol. 54, no. 3, Oct. 2014, pp. 95-124, doi:10.14456/ndj.2014.28.