The Geometric Brownian Motion of Indosat Telecommunications Daily Stock Price During the Covid-19 Pandemic in Indonesia

Abstract One of the major telecommunication and network service providers in Indonesia is PT Indosat Tbk. During coronavirus (COVID-19) pandemic, daily stock price that company was influenced by government policies. This study addresses data movement from February 5, 2020 to 2021, resulted 243 data, using Geometric Brownian motion (GBM). The stochastic process realization this fluctuates increases exponentially, especially 40 latest data. Because situation, transformed into log 10 calculated its return. As a result, weak stationary variance obtained. Furthermore, only December 7, 2021 fulfill GBM assumption return, as R t 1 * , = 2 3 … 40 . main idea adding datum one much 10% – 15% total ${R_{t_1^*}}$?> , starting 4, backwards. Following procedure, based on 3% < p -value 10%, shows can be included so $t_1^* - 4. 3, 2,\,…\,40$?> − 4. form five other groups, ${R_{t_2^*}},\,…\,\,{R_{t_6^*}}$?> 6 Considering Mean Absolute Percentage Error (MAPE) amount each group, ${R_{t_6^*}}$?> selected for modelling. Thus, succeeded representing second most popular Indonesian during COVID-19 pandemic.