I need to find out how many month our customers meet our mutual contract by paying agreed amount every month. E.g. we have a contract saying they should pay EUR xx every month for 12 month. Many of them will stop paying before the 12 month and I need to find the average number of months they are paying.
My payment table looks like this
Costumer Paid Date(MonthYear)
A 200 01-2009
A 200 02-2009
A 200 03-2009
A 200 04-2009
B 500 01-2009
B 500 02-2009
B 500 03-2009
B 500 04-2009
B 500 05-2009
B 500 06-2009
B 500 07-2009
B 500 10-2009
B 500 11-2009
B 500 12-2009
So customer A pays for 4 months and then stops and customer B pays for 7 months and then stops. He later picks up again after having skipped August and September but the ensuing payments shouldn't be included in the count as he broke his contract after 7 months. Average: 11/2 = 5,5 months.
I shall only calculate for customers who meet certain criteria which is in another table (contract has been signed, contract has started, contract has not expired etc)
Any ideas how I can find the average number of months they pay based on the above ?
