Percentage Change

Description

The terms “relative change” and “relative difference” are used to compare two quantities while taking into account the “sizes” of the things being compared. The comparison is expressed as a ratio and is a unitless number. By multiplying these ratios by 100 they can be expressed as percentages.
A percentage change is a way to express a change in a variable. It represents the relative change between the old value and the new one.
When the variable in question is a percentage itself, it is better to talk about its change by using percentage points
(A percentage point (pp) is the unit for the arithmetic difference of two percentages. e.g. going from 1% to 9% is an 8 percentage point increase)