What is the correct way of calculating the average percentage in this scenario?
Assume that there two people working in a call centre: PersonA and PersonB.
They are both waiting for calls in separate locations.
I want to calculate the average amount of time spent waiting overall.
The scenario is this:
PersonA spends 50 minutes out of 100 (50.00%) waiting for calls to come in (the other 50 minutes were spent on calls).
PersonB spends 900 minutes out of 1000 (90.00%) waiting for calls to come in (the other 100 minutes were spent on calls).
My question is this: what is the correct way to calculate the average waiting time across both people?
Should I take an average of their respective time-spent-waiting percentages or should I take into account their collective total available time when working this out?
I have tried taking the average of PersonA's and PersonB's time-spent-waiting percentages, which seems plausible:
AVERAGE(0.5, 0.9) = 0.7 (70.00%)
I understand this to mean that, on average, the time spent waiting was 70.00% across both people.
But then, taking into consideration PersonA and PersonB's total available times when calculating this also seems plausible:
950 minutes (waiting) / 1100 minutes (total available time) = 86.36%
Which I understand to mean that, out of 1100 minutes of total availability, the average amount of time spent waiting across both people was 86.36%.
What is the difference, and which is the correct way to calculate this in this scenario (and why)?
$\endgroup$ 191 Answer
$\begingroup$You need to average over the same time interval. Take the time interval to be 1000 minutes. A spends 50% of that, 500 minutes, waiting. B spends 90% of that, 900 minutes, waiting. They spend a total of 500+ 900= 1400 minutes waiting out of a total of 2000 minutes. Together they average 1400/2000= .7 or 70% of their time waiting. That is, of course, exactly the same as (50+ 90)/2= 70 since the "base" in both cases is the same- time. Your second calculation is wrong because you used different time intervals.
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