Is there a formula for the percent change over multiple periods or will I have to calculate the percent change for each previous period versus the year prior?

Eric,

You are best to report the change each year as a percentage over the previous year. If you want just one number you can calculate (1349-900) ÷ 1349 × 100 = 33.28 and say "Over the period from 2002 to 2006 the value decreased by 33.28% of the 2002 value."

Penny

Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.