weighted average question


No cake for spunky
This is a really simple question, but I am sick today and having a hard time concentrating.

For the course of the year we have a number of customers and an average number of days on the WL. We generate this 4 times a year. The number of customers varies from quarter to quarter. We want to generate an average for the entire year.

I know you do not simply add up the number of days on the WL in the 4 quarters and divide by 4 because you have a different number of customers in each quarter. But I can not for the life of me remember how to do this.

This is how many we have for the 4 quarters.

customers 55 days 71
215 days 98
293 days 133
557 days 332


Less is more. Stay pure. Stay poor.
WL = wait list. If so, I am a really good guesser!

Do you need a dispersion parameter as well?

You can just calculate the average for the full year! Otherwise, the calculate you want to calculation you are trying to get is actually the average quarterly WL time, not the annual average WL time.


No cake for spunky
I don't understand your comment hlsmith. We ran the numbers at 4 points in the year (4 quarters). Because of the way the report is run we need to average the 4 quarterly reports for the yearly results, not run a new report with the yearly results. I believe the correct answer now is to multiply the customers each quarter times the waitinglist days for quarter, sum this number over all 4 quarters, than divide by the summed total (for all 4 quarters) of customers.


No cake for spunky

Actually I did that than took your suggestion and ran the data from scratch for the whole year. I just had to convince my manager that was a good idea rather than averaging the 4 quarters.

My sql skills are getting better.