I have a positive start value in 1996 of +1200 million and a negative end value in 2008 of -7500 million. The values are actual trade balances for a group of specific products. In 1996 the country exported 1200 million more than it imported and in 2008 the country imported more than it exported. How do I calculate the rate of change from 1996 to 2008? I know that compound growth will not work because of the negative end value. Any help please.