Uji validitas dan reliabilitas kuesioner the 15-item myasthenia gravis quality of life scale versi bahasa indonesia mg-qol15 ina dalam penilaian kualitas hidup pasien miastenia gravis = Validity and reliability test of the indonesian version of the 15-item myasthenia gravis quality of life scale mg-qol15 ina for quality of life assesment in myasthenia gravis patients