Estimate the index of Corruption in Iran Using Fuzzy Logic and Investigation of its Relationship with the Underground Economy using Hsiao causality test

In recent years, the factors influencing the corruption, have attracted more attention among the economists and policy makers, because corruption is one of the main obstacles to economic growth, declining government legitimacy, increased illegal activity and political instability of countries. Therefore the purpose of this study is to estimate the index of corruption in Iran during the period of 1978-2013. In this study, to estimate the index of corruption the fuzzy logic (Fuzzy Logic) that is popular in applications such as ambiguous time series is used. The results show that the index of corruption have been fluctuating in some years but in recent years the trend index of corruption has been upward. The other results of this study show that a two-way causal relationship between underground economy and corruption existed in Iran.