formula which picks the best sales person using hours worked, calls answered & sales

Hi Guys

I am trying to create a ratio or formula which calculates the most effective sales person based on hours worked, calls answered, successful sales for those calls, revenue and margin.The formula would have to take the following into consideration:

- sales transactions can vary with regards to their value. Therefore a sales person can be lucky and convert a high value sale. Therefore revenue and margin can be high despite having fewer calls and a successful call rate than another person.
- Sales person commit different working hours. So for example one could work 10 while another 4 hours per day.

Can you help create an ideal formula to find the most effective sales person?

Kind regards
Chris

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