Mumbai: Folios in index funds saw more than a fourfold jump to 1.53 million in August this year from 345,000 in March 2020, according to data from the Association of Mutual Funds in India (AMFI). Assets under management surged more than five times during this period, to Rs 28,093 crore from Rs 5,815 crore.Financial planners said investors turned to index funds mainly because of the inability of active fund managers to outperform the benchmark indices, especially in the large-cap category. Many first-time investors also chose passive funds due to their low cost, ease of understanding and no fund manager bias.