Question: how to calculate average percentage change over time?
Answer: Step 1: Calculate the Individual Percent Changes. For the above example, we have. [(1,100 - 1,000) ÷ (1,000)] × 100 = 10% for the first year, ... 
Step 2: Sum the Individual Percentages. 10 + 9.09 + 8.33 + 7.69 + 7.14 = 42.25.
Step 3: Divide by the Number of Years, Trials, Etc. 42.25 ÷ 5 = 8.45% References.