A. A. Khin, W. H. Chau, U. L. Yean, O. C. Keong, and R. L. Leh Bin, “Examining between Exchange Rate Volatility and Natural Rubber Prices: Engle-Granger Causality Test”, IJEFI, vol. 7, no. 6, pp. 33–40, Dec. 2017.