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The Math of Contact Center Staffing
2016 Annual Conference
© Copyright Reynolds/Klenke 2015
Session Overview
In this session, you will learn to: Outline the implications of overstaffing and understaffing. Identify the unique characteristics and requirements for
inbound call center staffing. Identify staffing models for inbound call centers. Calculate staff requirements to meet service goals. Identify basic call center staffing tradeoffs. Identify small versus large group size considerations. Outline steps for staffing for outbound calls, emails, and
chat contacts.
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Call Center Staffing
Call center success depends on getting the
right number of people for each period of the day
to answer incoming contacts at a desirable level of service while
minimizing cost
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Implications of Getting it Wrong
Overstaffing
Understaffing
When considering the impact of adding or subtracting staff, consider the impact on three main stakeholder groups:
Customers Frontline Staff Management
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Impact on The Customer
Overstaffing
Faster service
Expectation of future service
Understaffing
Long delays
Reduced quality of service
Abandoned calls
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Service Implications
Think about the wait in queue from the customer’s perspective.
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Queue Perspectives
In-Person Queue
See the queue
Select a queue
Watch progress
Estimate time
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Queue Perspectives
Telephone Queue
Invisible queue
Limited choices
No sign of progress
No idea of time
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Impact on Frontline Staff
Overstaffing
More idle time
Less productive
Boredom
Understaffing
Less idle time
More stress
Angry callers
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Impact on Management
Overstaffing
Excessive costs
Lower productivity
Understaffing
Unhappy callers
Unhappy staff
Higher phone costs
Abandoned calls
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Calculating Contact Center Workload
Workload = Call Volume x Average Handle Time (AHT) (expressed in hours of work in a one-hour period)
For AHT in minutes, divide by 60 / For AHT in seconds, divide by 3600
Example: 400 calls per hour, AHT = 180 seconds 400 x 180 / 3600 = 20 hours or erlangs
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Workload Arrivals
20 Hours Sequential Versus Random Workload
How many staff?
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Workload Arrivals
20 Hours Sequential Versus Random Workload
20 staff > 20 staff
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Defining Speed of Answer Goals
Service level x% of calls answered in y seconds Average speed of answer (ASA) (Average delay of all calls – including calls with no wait)
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What is your service goal?
When did you set the goal?
How do you measure success?
How do you compare to others?
A Discussion About Setting Service Goals
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A View of Service Level
Time of Day Call Volume Daily % SL (in 20 sec)
6:00 – 7:00 85 4.5% 100%
7:00 – 8:00 90 5.0% 95%
8:00 – 9:00 95 5.5% 95%
9:00 – 10:00 145 8.0% 90%
10:00 – 11:00 185 10.0% 75%
11:00 – 12:00 195 10.5% 70%
12:00 – 1:00 165 9.0% 80%
1:00 – 2:00 185 10.0% 80%
2:00 – 3:00 220 12.0% 65%
3:00 – 4:00 210 11.0% 70%
4:00 – 5:00 145 8.0% 80%
5:00 – 6:00 125 6.5% 85%
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Staffing for Service Goal with Erlang C
1. Calculate staff workload. Call volume: 400 calls Talk time: 150 sec Wrap-up time: 30 sec AHT: 180 sec Workload = 400 x 180 / 3600 sec/hour = 20 hours
2. Define service goal. Desired speed of answer = ASA <30 seconds
3. Determine staff to meet service objective.
© Copyright Reynolds/Klenke 2015
Need model to predict what will happen in simple incoming call situation with:
Erlangs of workload
Varying staffing levels
Erlang C assumptions – Random call arrivals – Infinite queue
Other traffic models – Erlang-Engset (smooth workload) – Equivalent Random Theory (peaked traffic)
Staffing Calculations
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Erlang C will fit most simple call center staffing scenarios
Erlang C Formula:
Staffing Calculations
where:"A is the total traffic offered in units of erlangs!N is the number of servers!PW is the probability that a customer has to wait for service
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Staffing with Erlang C
Workload Hours
Number of Staff
ASA Service Level (30 sec)
Staff Occupancy
20 21 137 sec 35% .95 20 22 51 sec 59% .91 20 23 25 sec 75% .87 20 24 13 sec 85% .83 20 25 7 sec 91% .80 20 26 4 sec 94% .77
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Evaluate staffing decisions with these tradeoffs in mind:
• Customer Impact
What is delay time with +/- one agent?
• Frontline Impact
What is occupancy rate with +/- one agent?
• Management Impact
What are the financial implications?
Staffing Tradeoffs
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Service Tradeoffs
Workload Hours
Number of Staff
ASA Service Level (30 sec)
Staff Occupancy
20 21 137 sec 35% .95 20 22 51 sec 59% .91 20 23 25 sec 75% .87 20 24 13 sec 85% .83 20 25 7 sec 91% .80 20 26 4 sec 94% .77
What is the impact on service when staff are added or subtracted?
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Productivity Tradeoffs
Workload Hours
Number of Staff
ASA Service Level (30 sec)
Staff Occupancy
20 21 137 sec 35% .95 20 22 51 sec 59% .91 20 23 25 sec 75% .87 20 24 13 sec 85% .83 20 25 7 sec 91% .80 20 26 4 sec 94% .77
What is the impact on occupancy when staff are added or subtracted?
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Financial Tradeoffs
Workload Hours
Number of Staff
ASA Staff Occupancy
20 21 137 sec .95 20 22 51 sec .91 20 23 25 sec .87 20 24 13 sec .83 20 25 7 sec .80 20 26 4 sec .77
86 seconds
What is the impact on revenues and costs when staff are added or subtracted?
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Telephone Costs
1. Determine additional queue time with missing staff. ASA of 137 versus 51 seconds = 86 seconds per call
2. Multiply by number of calls. 400 calls x 86 seconds per call = 34,400 seconds
3. Calculate number of minutes. 34,400 / 60 = 573 minutes of additional queue time
4. Apply average cost per minute of telephone service. 573 minutes @ 3¢ per minute = $ 17.19 per hour
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Impact of Size
Calls /Hour
Staff Workload
Number of Staff
Occupancy Level
Service Level
400 20 hours 23 87% 75% 400 20 hours 24 83% 85% 400 20 hours 25 80% 91%
800 40 hours 44 91% 78% 800 40 hours 45 89% 85% 800 40 hours 46 87% 90%
1600 80 hours 85 94% 79% 1600 80 hours 86 93% 85% 1600 80 hours 87 92% 89%
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Staffing for Other Contacts
Communications with customers occurs over many channels:
Inbound phone calls Outbound phone calls Email Chat
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Calculating Contact Center Workload
Workload = Contact Volume x Average Handle Time (AHT) (expressed in hours of work in a one-hour period)
Incoming Call Example: 400 calls per hour, AHT = 180 seconds 400 x 180 / 3600 = 20 hours or erlangs
Workload calculations be different for: Outbound calls Email Chat
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Calculating AHT for Outbound Calls
In addition to talk time and after-call work, consider front-end set-up time for outbound calls.
Components of Set-Up Time: Looking up number Dialing Waiting for network connect Waiting for customer connect Time on non-connects
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Call Volume Type of Call Set-up Time Talk Time
40 Answered call
32 sec 135 sec
40 Voice mail
34 sec 0 sec
15 Busy signal
22 sec 0 sec
5 No Answer
46 sec 0 sec
100 calls All Calls 3200 sec 5400 sec
Calculating Set-Up Time
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In this example, 37% of staff time has been spent in just placing the calls. Don’t forget to include this in handle time calculations.
Manual Dialing Results:
3200 seconds set-up
5400 seconds talk time
8600 seconds total time
Call Set-up Time
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Calculating Workload for Other Contacts
Considerations for Email Handle Time:
Is history available? When does email begin and end?
Considerations for Chat Handle Time:
Is history available? How many simultaneous chats?
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Selecting a Staffing Model
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Contact Type Work Pattern Model
Outbound calls Sequential Ratio
Email Sequential Ratio
Chat Random Erlang C (modified)
Session Review
In this session, you learned to: Outline the implications of overstaffing and understaffing. Identify the unique characteristics and requirements for
inbound call center staffing. Identify staffing models for inbound call centers. Calculate staff requirements to meet service goals. Identify basic call center staffing tradeoffs. Identify small versus large group size considerations. Outline steps for staffing for outbound calls, emails, and
chat contacts.
© Copyright Reynolds/Klenke 2015