Calculating required FTE for Email

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Calculating required FTE for Email
Hi group, I'm using the same Erlang model I use for voice to work out required FTE for email with the following parameters:
* 336 mails per day
* AHT = 480 seconds
* SLA is 80% in 4 hours (14400 secs)
Result gives me roughly 8.6 FTE (once I factor in 85% occupancy and 19.5% shrinkage and a workday of 9 hours), which I validated using this site's Erlang calculator.

The challenge I have is that when I change the SLA component from 80% in 4 hours to 12 hours, the FTE requirement only drops to 8.4 FTE. If I change it to 48 hours, it doesn't change at all from 8.4 FTE.

I need to be able to either confirm if this is correct or not, and if it's correct, be able to explain why it's correct. On face value, if I want to answer emails in 4 hours versus 48 hours, surely I'm going to need more people, so why doesn't the formula reflect that? Or am I missing something fundamental?

I've never tried to work this out before as my background has been pretty much voice, so any help would be greatly appreciated.

Pete

Helper

Call Centre Helper

Looks correct to me
Extending the response time only shows a great impact on the shorter time lags. There is very little difference in FTE between 4 hours and 48 hours. which is why it always surprises me that people don't have lower targets.

Plus if you don't resolve within 4 hours it can often trigger a phone call which drives up demand even higher.

Could you expand further please
Thanks for your reply Jonty, I don't quite understand though. In a voice scenario, if you extend the response time, it very clearly shows fewer people required. Why is the same not true for email? I suspect it has something to do with the relatively short AHT compared to the relatively long response time, so in the 4 hour window, in theory, you should have fairly good throughput and less backlog than in voice where the response time is much shorter than the AHT typically.

am I on the right track? As I mentioned, I'm happy with the outputs of the formula, but I have to explain it to people who aren't ion this game, so any help to simplify the explanation would be appreciated.

Helper

Call Centre Helper

The ratio of response time to duration is different
The ratio of response time to duration is different. The same would hold for voice or for a phone call.

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