Modeling Iran`s Underground Economy: A Fuzzy Logic Approach

The underground economy has long been of interest to economists and has devoted extensive studies to itself in economic literature. Through fuzzy logic approach in present research, we estimated the size of underground economy of Iran over the period of 1978-2010. For this purpose and according to theoretical bases and previous studies, variables such as GDP per capita, ratio of direct taxes to GDP and an index of business environment for considering the effect of institutional structures have been used as the most important explanatory variables for estimating country's underground economy. For considering the quality of institutions in this research we have used a local index for the first time compared with other internal studies. Our results indicate an oscillatory trend as the average of relative and absolute size of underground economy has decreased during the years of first development plan compared with period of war and revolution but increased during the second plan compared with the first one. Also it has decreased over the years of third plan in comparison with the second one but again it has increased during the fourth development plan. According to the results, the average of relative size of underground economy to official output during the years of war and revolution, first, second, third and the fourth development plan was approximately estimated 21, 12, 29, 19 and 20 percent respectively. During the entire period it was approximately 20 percent.