The formula for percent change (PC) is:
((end count - initial count) / initial count) * 100
On the Statistic tab in a Frequency session, you can set PC End Points to "One Year" or "Two-Year Average". If PC End Points is set to "One Year", then the initial count is the first year of the range and the end count is the last year. If PC End Points is set to "Two-Year Average", the software uses an average of the initial two years and last two years in the range for PC End Points.