webinar on call center wfm: why is erlang c unsuitable for call … · 2020. 3. 30. · erlang c...
TRANSCRIPT
Webinar on call center WFM:Why is Erlang C unsuitable for call center
safety staffing?
March 27, 2020Ger Koole, PhD
Steps in agent scheduling
• What is load*? • Load = FC x AHT in same time unit• Equal to # fully active agents needed to work away incoming work• E.g., FC = 60 in quarter = 4/min , AHT = 3 minutes: load = 4 x 3 = 12• Load has no dimension: commonly called Erlang
Workload forecasting Safety staffing Agent scheduling(net) head count(forecasted) load
*See Glossary @ WFM fellowship for definitions
Safety staffing
• How many agents to schedule? • Forecasted load is not enough because of
fluctuations in actual load• How much safety staff* to schedule to
mitigate the impact of fluctuations?• Safety staff = The additional # of agents
needed to reach SL• How to compute? Erlang C• Note: Safety staff ≠ shrinkage• Shrinkage is added when scheduling
Fluctuations in arrivals
Fluctuations in load
*equivalent to safety stock in logistics
forecasted load
Erlang C calculations
FC = 4AHT=3 14
SL = 61%/20s, ASA = 43s
FC + AHT + agents → SL, ASA• Invented by A.K. Erlang (1878-1929)
• Gives SL and ASA*
• Takes fluctuations in input into account
• Example: safety staffing = 2, total = load + safety = 14
• Still some calls have to wait and SL < 100%
*Online calculator on CCmath.com
Erlang C calculations
FC = 4AHT=3 16
SL ≥ 80%/20s
FC + AHT + SL → agents
• Also for backward calculation: determines safety staffing for given SL or ASA
Leads to some overstaffing
FC = 4AHT=3 16
SL = 87%/20s, ASA = 9s
FC + AHT + agents → SL, ASA
Erlang C: disadvantages
• Erlang C gives SL “forecast” – without fluctuations!• Erlang C was invented before call centers existed, does not “model”
all aspects – especially abandonments
SL fluctuations
• Erlang C predicts SL – without fluctuations!• Actual SL fluctuates – 80% is luck !• Result: if you staff for 80% you get
a SL < 80% in 50% of the cases• How to quantify? • Simulation• Demo*
• Erlang C = very long simulation (by a quick calculation)
*Simulation tool: www.gerkoole.com/CCO/1-skill-simulator.php
SL fluctuations
• Fluctuations are less:• over longer periods• in bigger call centers
• But decrease slowly… (with √)• Real-time performance management remains necessary• Also because of unforeseen changes in load & capacity
Calculations from PhD thesis Alex Roubos
Abandonments
• Erlang C does not tell the whole story…• What happens when a call center is
understaffed?• In reality calls abandon
• In all situations• Especially when understaffed
• Solution: Erlang X
Erlang X
• Gives abandonment %
• Requires average patience (“willingness-to-wait”)
• Also:• Redials• Finite # of lines• Non-integer staffing
• Less staffing required than Erlang C
• Gives always good answer – also when understaffed
FC = 4AHT=3 14
SL = 77%/20s
Erlang X
av. patience = 5 min
ab = 4%
FC = 4AHT=3 15
SL ≥ 80%/20s
av. patience = 5 min
ab = 3%
Redials
• Even with 100% redials higher SL than Erlang C
FC = 4AHT=3 14
SL = 77%/20s
av. patience = 5 min ab = 4%
FC = 4AHT=3 14
SL = 73%/20s
av. patience = 5 min ab = 5%
50%
Excel Office 365 demo
Learning more
• www.wfmfellowship.com• Online trainings for
workforce management• At you own time & place• Videos, exercises,
assignments • Supported by CCmath
professionals• Subscribe online or at
Excel CCmath Erlang add-in
• Windows add-in• Runs locally• Requires software to be installed (xla, dll)
• Office365• Ready in a few weeks!• Requires add-in (xml)• Connects to CCmath server
• Implemented in CCmath WFM cloud suite
• Information: [email protected]
Next week
• Friday April 3, 16:00 AMS time• Subject: to be determined• Suggestions: [email protected]
• Questions? Chat or voice