nurse rostering focus on models or algorithms?...joint work with mihail mihaylov and pieter smet...
TRANSCRIPT
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NURSE ROSTERINGFocus on models oralgorithms?Greet Vanden BergheKU LeuvenCHOIR in Practice, 22 November 2013
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Taxonomy personnel rostering
A.T. Ernst et al. (2004), Staff scheduling and rostering: A review ofapplications, methods and models, EJOR 153:3-27
• RosteringI Demand modellingI Shift based demand
• Days off scheduling
• Shift scheduling
• Task assignment
• Staff assignment
J. Van den Bergh, J. Belien, P. De Bruecker, E. Demeulemeester, L. DeBoeck (2013), Personnel scheduling: A literature review
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Definition
Nurse rostering
Distribute shifts over the qualified members of staff in order to meet thecoverage requirements, taking into account legal and contractualconstraints and personal preferences.
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Datasets
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Nurse rostering competition 2010
S. Haspeslagh et al. (to appear)The first international nurse rostering competition 2010,Annals of OR
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Web of Knowledge
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10 most cited papers
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Health care
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Logistics
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Surveys
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Algorithms
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Psychology
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Software
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Where is the theory?
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Vehicle routing
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Scheduling
Peter Brucker, University of Osnabruck: 29 pages theory
• Single machine problems
• Parallel machine problems without preemption
• ...
• Serial batching problems
• ...
• Flow shop problems with transportation times and a single robot
• ...
• Flow shop problems with a single server
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Scheduling
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Where is the theory?
NP-hard problem
• H.C. Lau (1996) On the complexity of manpower shift scheduling, Computers &OR, 23(1): 93-102
• T. Osogami, H. Imai (2000) Classification of various neighbourhood operationsfor the nurse scheduling problem, Lecture Notes in Computer Science, 1969:72-83
• M. Moz and M. Vaz Pato (2007) A genetic algorithm approach to a nursererostering problem (!reference to a Portugese proof), Computers & OR, 34:667-691
• P. Brucker, R. Qu, E.K. Burke (2011) Personnel scheduling: Models andcomplexity, EJOR 210 (3): 467-473
• M. Rocha, J.F. Oliveira, M.A. Carravilla (2013) Cyclic staff scheduling:optimization models for some real-life problems Journal of Scheduling, 16 (2):231-242
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Categorisation nurse rostering
P. De Causmaecker, G. Vanden Berghe (2011) A categorisation of nurserostering problems, Journal of Scheduling, 14(1): 3-16
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Where is the rest of the theory?
Personnel scheduling
Can personnel scheduling reach the same academic status as vehiclerouting, scheduling?
What do we need?
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Effort to establish theory
AI|RV N |Gformulated as integer minimum cost flow problems: polynomiallysolvable
Pieter Smet, Peter Brucker, Patrick De Causmaecker, Greet VandenBerghe (2013)
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Where are the applications?
Kellogg and Walczak (2007) Nurse Scheduling: From Academia toImplementation or Not?, Interfaces 37(4): 355-369
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Not ready yet
Current practice
Iterative academic approach
• Relevant, attractive problems
• Tailored algorithms
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A hard problem
Terminology
Personnel scheduling
Distribute shifts over the qualified members of staff in order to meet thecoverage requirements, taking into account legal and contractualconstraints and personal preferences.
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A hard problem
Time• scheduling horizon: 4 weeks, 1 month, 13 weeks, ...
constraints across subsequent horizons?• cyclic, semi cyclic, non cyclic schedules• shift types
start- and end time, overlapping shifts, deviating hours, interruptedduties
shift type from till
early 7:00 15:00day 8:00 17:00late 13:00 21:00night 21:00 7:00
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A hard problem
Personnel
• skillstraining, experience, responsibility, job description, multiple skills
• contractsfull time, part time (x %), night nurse, weekend nurse, etc.
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A hard problem
Personnel
• skills ... change over timetraining, experience, responsibility, job description multiple skills
• contracts ... change over timefull time, part time (x %), night nurse, weekend nurse, etc.
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A hard problem
Coverage requirements
• coverage = number of qualified personnel members per day and pershift type, for the entire scheduling horizon
• minimum coverage hard constraint?
• preferred coverage
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A hard problem
Constraints
• legal constraintse.g. minimum rest timehard constraints?
• organisational constraintse.g. no skill downgradinghard constraints?
• contractual constraintse.g. maximum 6 nights per month
• personal constraints/preferencese.g. free Wednesday afternoons
Any feasible solution to the problem?
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A hard problem
Evaluation of solutions
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A hard problem
Constraint classes
Counters e.g. number of working days
v(dwce,D′ ) = csv(dwce,D′ ) +∑
d∈D′pe,d
Series e.g. number of consecutive days worked
p(dwse) = w(dwse)∑d∈D
max
m(dwse)∑
i=0
pe,d+i
− m(dwse), 0
Successive series e.g. number of free days after night shifts
Conditional constraint.
P. Smet et al. (to appear) Nurse rostering: a complex example of personnel schedulingwith perspectives, Automated Scheduling: Real World Case Studies, Springer
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A hard problem
Consistent constraint evaluation
• constraint definition work stretches or patterns?
• continuity of series constraints regardless of the scheduling period(previous and upcoming planning period)
• contextual evaluation of constraints
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A hard problem
Example 1: Counters
Counter penalty
proportional to the constraint violation ... context?
• Employee request5 free days starting on Feb 1 for a ski vacation
• Grant either all days or not any at all
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A hard problem
Example 1: Counters
Counter penalty
proportional to the constraint violation ... context?
• Employee request5 free days starting on Feb 1 for a ski vacation
• Grant either all days or not any at all
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A hard problem
Example 2: Series
• weekdays: Mon - Fri
• weekend days: Fri - Mon
• weekend constraint:work full weekends
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A hard problem
Example 3: Successive series
Overtime
Overtime should be compensated within the next three months.
Interpretation?
1. start counting from the first minute of overtime
2. start counting from the shift assignment causing overtime
3. start counting from the first Monday after the minute/shift causingovertime
4. do not allow additional overtime before the previous overtime hasbeen compensated ... or not?
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A hard problem
Example 3: Successive series
Overtime
Overtime should be compensated within the next three months.
Interpretation?
1. start counting from the first minute of overtime
2. start counting from the shift assignment causing overtime
3. start counting from the first Monday after the minute/shift causingovertime
4. do not allow additional overtime before the previous overtime hasbeen compensated ... or not?
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A hard problem
Example 3: Successive series
Overtime
Overtime should be compensated within the next three months.
Interpretation?
1. start counting from the first minute of overtime
2. start counting from the shift assignment causing overtime
3. start counting from the first Monday after the minute/shift causingovertime
4. do not allow additional overtime before the previous overtime hasbeen compensated ... or not?
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A hard problem
Example 3: Successive series
Overtime
Overtime should be compensated within the next three months.
Interpretation?
1. start counting from the first minute of overtime
2. start counting from the shift assignment causing overtime
3. start counting from the first Monday after the minute/shift causingovertime
4. do not allow additional overtime before the previous overtime hasbeen compensated ... or not?
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A hard problem
Example 3: Successive series
Overtime
Overtime should be compensated within the next three months.
Interpretation?
1. start counting from the first minute of overtime
2. start counting from the shift assignment causing overtime
3. start counting from the first Monday after the minute/shift causingovertime
4. do not allow additional overtime before the previous overtime hasbeen compensated ... or not?
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A hard problem
Accurate data
• hard vs. soft constraints
• constraint weights
• implicit preferences
• agreement on the data description
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A hard problem
Quality of a solution
• monetized objectives
• weighted constraint violations
Weighted sum
WO =∑
∀n∈N∑
∀c∈C #violationsn,c ∗ weightc
• compensations? unfair objectives, fair variants? fairness measures?
Fairness measures
FO = maxn(qn)GO = qavg +
∑n∈N (|qavg − qn|)
RO = qavg +maxn(qn)−minn(qn)
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A hard problem
Weighted sum vs. fairness objectives
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A hard problem
Constraint weights
Mihail Mihaylov and Pieter Smet
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A hard problem
Constraint weights
joint work with Mihail Mihaylov and Pieter Smet
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A hard problem
Constraint weights
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A hard problem
Algorithmic trends
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Not an isolated problem
Float nurses
What is the problem with a pool of float nurses?
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Not an isolated problem
Workload vs. available staff
Feasible region
Pe
na
lty
Number of shifts to cover
Stefaan Haspeslagh, PhD, 2012
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Not an isolated problem
Workload vs. available staff
Feasible region
Pe
na
lty
Number of available nurses
Stefaan Haspeslagh, PhD, 2012
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Not an isolated problem
Workload
Wim Vancroonenburg
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Not an isolated problem
Tasks vs. shifts
Pieter Smet
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Not an isolated problem
Decision levels
• interaction with manpower planning, staffing
• quality of solutions cannot be evaluated without information aboutthe quality of solutions at the other levels
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Not an isolated problem
Staffing - scheduling
Komarudin
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Not an isolated problem
Experimental results
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Not an isolated problem
Why difficult?personnel schedulers have been doing it manually for years, why would itbe difficult to address the problem with a suitable optimisation approach?
• complexity?
• computation time?
• collection of correct information?
• consistent evaluation of the quality?
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Conclusions
A hard problem
automated personnel scheduling
• model: correct and sufficiently generic
• algorithm: produce an acceptable solution
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Conclusions
Acknowledgements
Patrick De Causmaecker, Edmund Burke, Sanja PetrovicPeter Brucker, Tim Curtois, Rong Qu, Pieter Smet, Burak BilginStefaan Haspeslagh, Fabio Salassa, Marie-Anne Guerry, Tim De FeyterKomarudin, Mihail Mihaylov, Wim VancroonenburgJan Christiaens, Jannes Verstichel
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