increase by a factor of n（基数词） 不是受影响增加了几倍

The annual output of the refrigerators has been increased by a factor of four since 1992. 【误译】自1992年以来，电冰箱的年产量增加了4倍。 【正确】自1992年以来，电冰箱的年产量增加了3倍。 说明： 若将上例改成The annual output of the refrigerators has been increased four times since 1992.其句意与上例相同。 但如果改成The annual output of the refrigerators has been increased by four times since 1992. 则意为“自1992年以来，电冰箱的年产量增加了4倍。”