When referring to a reduction in quantity or value, there are many different phrases that can be used in place of "decreased by". Some synonyms for decreased by include "diminished by", "lowered by", "lessened by", "reduced by" and "curtailed by". Additionally, phrases like "shrank by", "contracted by", "shortened by", "abridged by" and "narrowed by" can also be used to express a decrease in something. It's always important to vary your vocabulary in order to prevent redundancy and make your writing as clear and precise as possible. By opting for alternative expressions, you can add variety and interest to your language.