Decrease

Todasy's language tip helps with using the patterns that follow the noun decrease. Don’t use decrease of when you want to talk about what is decreasing. Use decrease in:

✗ The experiment has not led to the expected decrease of crime.
✓ The experiment has not led to the expected decrease in crime.
✗ There has been a decrease of the birth rate in the industrialized world.
✓ There has been a decrease in the birth rate in the industrialized world.

Use decrease of with a number or percentage, when you want to talk about the amount by which something decreases:

These emissions show a decrease of 21 percent over the past five years.

Source: Macmillan Language Tips