Isnaini, Bayutama, et al. “Estimating the Parameters of a Robust Geographically Weighted Regression Model in Gross Regional Domestics Product in East Java”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 48, no. 3, Sept. 2019, pp. 150-6, https://www.gssrr.org/JournalOfBasicAndApplied/article/view/10346.