Average Percentages

[Jgr4ng3]

Hello

I have a database that stores QA data, a percentage score is calculated and I was previously able to obtain an accurate average by agent percentage score.

However, now, the average percentages (which are calculated in a query) are completely inaccurate. For example the majority if not all average scores should be between 80%-100% however I've got 30% averages which I know are incorrect on analysing the data.

Any ideas how an average is not an average ?

Cheers, Jake.

 

[plog]

Yes, its called weighting. It matters when you do the percentage calculation. Look at this data:

Sales, SalesCalls, SalesPercent
1,1,100
3, 75, 4
6, 24, 25

SalesPercent is that rows Sales field divided by that rows SalesCall field. If you average the SalesPercent field you get 43%. But if you add up the Sales field and then divide by the sum of all SalesCalls you get 10%.

The correct average is 10% because row 2 should have 75 times more weight than row 1. When you just average the percentages they have equal weight.

Percentage calculations should be the last calculation you do on data. You should never average percentages unless the denominator in all the average calculations of the percentages are the same.

 

[Jgr4ng3]

Right.. I dont understand why it happens, only that it does and the result. Have now amended my calculations - thanks for your help!

 

[Brianwarnock]

Plog explained why it happens. You should study his post and understand it else you will make the same or similar mistakes in the future.

Brian

 

[Jgr4ng3]

Plog explained why it happens. You should study his post and understand it else you will make the same or similar mistakes in the future.

Brian

It makes perfect sense now that it has been edited. Thanks Plog.

 

[plog]

I edited it 7 minutes after I initially posted it and 2 and a half hours before your initial response to it.

 

[Jgr4ng3]

I edited it 7 minutes after I initially posted it and 2 and a half hours before your initial response to it.

And I read your post immediately and left the tab open until I replied 2 and a half hours later, meaning I had not refreshed the page and did not see your edit until I had posted the reply.