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ger.koole@vu.nl
ger@gerkoole.com

address @ VU

Office
Room 9A-61 at 9th floor in "Nieuw Universiteitsgebouw"



Postal address
Department of Mathematics
Vrije Universiteit Amsterdam
De Boelelaan 1111
1081 HV Amsterdam
The Netherlands

Submitted papers:

• Optimal contact center staffing and scheduling with machine learning (with Siqiao Li and Qingchen Wang).
• Waiting-time distributions in blended multi-server queues with impatient customers (with René Bekker, Petra Vis and Bartlomiej Zaber).

Refereed papers:

• A practice-oriented overview of call center workforce planning (with Siqiao Li).
  Stochastic Systems 13(4):479-495, 2023.
• Optimal call center forecasting and staffing (with Sihan Ding).
  Probability in the Engineering and Informational Sciences 36(2):254-263, 2022.
• Front-office multitasking between service encounters and back-office tasks (with Benjamin Legros, Oualid Jouini and Zeynep Aksin).
  European Journal of Operational Research 287(3):946-963, 2020.
• Should we wait before outsourcing? Analysis of a revenue-generating blended contact center (with Benjamin Legros and Oualid Jouini).
  Manufacturing & Service Operations Management 23(5):1118-1138, 2020.
• Blended call center with idling times during the call service (with Benjamin Legros and Oualid Jouini).
  IISE Transactions 50(4):279-297, 2018.
• A uniformization approach for the dynamic control of multi-server queueing systems with abandonments (with Benjamin Legros and Oualid Jouini).
  Operations Research 66(1):200-209, 2018.
• Flexible staffing for call centers with non-stationary arrival rates (with Alex Roubos and Sandjai Bhulai).
  In Markov Decision Processes in Practice (Richard Boucherie and Nico van Dijk, eds), Springer, 2017.
• Optimal scheduling in call centers with a callback option (with Benjamin Legros and Oualid Jouini).
  Performance Evaluation 95:1–40, 2016.
• On the estimation of the true demand in call centers with redials and reconnects (with Sihan Ding and Rob van der Mei).
  European Journal of Operational Research 246(1):250-262, 2015.
• Optimization of overflow policies in call centers (with Bo Nielsen and Thomas Nielsen).
  Probability in the Engineering and Informational Sciences 29(3):461-471, 2015.
• Adaptive threshold policies for multi-channel call centers (with Benjamin Legros and Oualid Jouini).
  IIE Transactions 47(4):414-430, 2015.
• Dynamic call center routing policies using call waiting and agent idle times (with Wyean Chan and Pierre L'Ecuyer).
  Manufacturing & Service Operations Management 16(4):544–560, 2014.
• Performance indicators for call centers with impatience (with Oualid Jouini and Alex Roubos).
  IIE Transactions 45(3):341-354, 2013.
• First in line waiting times as a tool for analyzing queueing systems (with Bo Nielsen and Thomas Nielsen).
  Operations Research 60(5):1258-1266, 2012.
• Service level variability of inbound call centers (with Alex Roubos and Raik Stolletz).
  Manufacturing & Service Operations Management 14(3):402-413, 2012.
• Staffing a call center with uncertain non-stationary arrival rate and flexibility (with Shuangqing Liao, Christian van Delft and Oualid Jouini).
  OR Spectrum 34(3):691-721, 2012.
• A note on profit maximization and monotonicity for inbound call centers (with Auke Pot).
  Operations Research 59(5):1304-1308, 2011.
• Queues with waiting time dependent service (with René Bekker, Thomas Nielsen and Bo Nielsen).
  Queueing Systems 68(1):61-78, 2011.
• Online scheduling policies for multiclass call centers with impatient customers (with Oualid Jouini, Auke Pot, and Yves Dallery).
  European Journal of Operational Research 207:258-268, 2010.
• A simple staffing method for multi-skill call centers (with Auke Pot and Sandjai Bhulai).
  Manufacturing & Service Operations Management 10:421-428, 2008.
• Simple methods for shift scheduling in multi-skill call centers (with Sandjai Bhulai and Auke Pot).
  Manufacturing & Service Operations Management 10:411-420, 2008.
• Approximating multi-skill blocking systems by hyperexponential decomposition (with Geert Jan Franx and Auke Pot).
  Performance Evaluation 63:799-824, 2006.
  
• Scaling and comparison of fluid limits of queues applied to call centers with time-varying parameters (with Tania Jiménez).
  OR Spectrum 26:413-422, 2004.
  
• A formula for tail probabilities of Cox distributions.
  Journal of Applied Probability 41:935-938, 2004.
  
• Telephone call centers: Tutorial, review, and research prospects (with Noah Gans and Avishai Mandelbaum).
  Manufacturing and Service Operations Management 5:79-141, 2003.
  
• Optimal shift scheduling with a global service level constraint (with Erik van der Sluis).
  IIE Transactions 35:1049-1055, 2003.
  
• A queueing model for call blending in call centers (with Sandjai Bhulai).
  IEEE Transactions on Automatic Control 48:1434-1438, 2003.
  
• Queueing models of call centers: An introduction (with Avishai Mandelbaum).
  Annals of Operations Research 113:41-59, 2002.
  
• Managing uncertainty in call centres using Poisson mixtures (with Geurt Jongbloed).
  Applied Stochastic Models in Business and Industry 17:307-318, 2001.
  
• On optimal call admission control in a resource-sharing system (with Eitan Altman and Tania Jiménez).
  IEEE Transactions on Communications 49:1659-1668, 2001.
  

Other scientific papers:

• A simple solution for optimizing weekly agent scheduling in a multi-skill multi-channel contact center (with Siqiao Li and Oualid Jouini). Proceedings of the 2019 Winter Simulation Conference.
• A method for estimation of redial and reconnect probabilities in call centers (with Sihan Ding and Rob van der Mei). Proceedings of the 2013 Winter Simulation Conference.
• Call center capacity allocation with random workload (with Shuangqing Liao, Christian van Delft, Yves Dallery, and Oualid Jouini).
  Proceedings of the 2009 International Conference on Computers & Industrial Engineering, July 6-8, Troyes, France.
• Approximate dynamic programming in multi-skill call centers (with Auke Pot).
  Proceedings of the 2005 Winter Simulation Conference.
• Performance analysis and optimization in customer contact centers.
  Proceedings of QEST 04, Enschede, pages 2-5, 2004.
• Routing heuristics for multi-skill call centers (with Auke Pot and Jérôme Talim).
  Proceedings of the 2003 Winter Simulation Conference, New Orleans, pages 1813-1816, 2003.
• The mathematics of call centers.
  ``Research highlight'', Biennual report Stieltjes Institute, pages 31-35, 2000/2001.
• Exponential approximation of multi-skill call centers architecture (with Jérôme Talim).
  In Proceedings of QNETs 2000, Ilkley (UK), pages 23/1-10, 2000.

Publications in the professional literature:

• Posts at WFManagement blog.
  2013.
• Errors in Erlang97 Excel add-in module/Fouten in Erlang97 Excel add-in module (with Karin van Eeden and Edwin van der Hilst).
  Telecommerce Nieuwsbrief week 4, 23 January 2013.
• WFM - Kosten, winst, SL en klanttevredenheid (with Annemiek van Moorst).
  Call Center Magazine 11(6):14-16, 2005.
• WFM en de kwaliteit van data (with Annemiek van Moorst).
  Call Center Magazine 11(4):14-16, 2005.
• Schaalvoordeel en skills bijten elkaar (with Annemiek van Moorst).
  Call Center Magazine 11(2):14-15, 2005.
• WFM: goede voorspelling noodzakelijk maar niet voldoende (with Annemiek van Moorst).
  Call Center Magazine 11(1):16-18, 2005.

Popular-scientific articles:

• Over wiskundig modelleren en call centers.
  Nieuwe Wiskrant 20(3):8-12, 2001.

Interviews:

Books:

• Call center optimization.
  MG books, Amsterdam, 2013.
  
• Optimization of business processes.
  Lecture notes.
  

Editorial work:

• Special issue on call center management.
  Management Science 54(2), 2008.

Press articles:

• Zwaarder geschut op planning nodig.
  Telecommerce Magazine 06, 2011.