pith. sign in

arxiv: 2311.11279 · v3 · submitted 2023-11-19 · 🧮 math.PR

Staffing under Taylor's Law: A Unifying Framework for Bridging Square-root and Linear Safety Rules

Pith reviewed 2026-05-24 05:28 UTC · model grok-4.3

classification 🧮 math.PR
keywords staffing rulesTaylor's lawover-dispersiondoubly stochastic Poisson processsafety staffingheavy trafficservice levelarrival processes
0
0 comments X

The pith

Staffing levels for over-dispersed arrivals scale as a power of the nominal load between the square-root and linear rules, with the exponent set by the Taylor's law parameter.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper constructs a doubly stochastic Poisson process model for arrivals that obey Taylor's law, linking variance to mean via a power relationship, and that also exhibit decaying temporal correlations between disjoint intervals. From this model it derives a closed-form staffing formula that meets a target service level. The formula shows the required safety staffing grows as a power of the nominal load, where the power lies between one-half and one according to the over-dispersion strength. A reader would care because the same model recovers the familiar square-root rule when arrivals are Poisson and the linear rule when over-dispersion is strong, thereby unifying the two classical prescriptions under a single empirical regularity. Numerical tests on both simulated and real arrival traces confirm the new rules outperform square-root, linear, and other alternatives.

Core claim

Using a doubly stochastic Poisson process whose variance-mean relationship follows Taylor's law and whose temporal correlations decay appropriately, the paper derives a closed-form staffing formula under which the safety level grows as a power of the nominal load; the exponent lies between 1/2 and 1 according to the degree of over-dispersion, establishing Taylor's law as the dominant driver of staffing requirements in heavy traffic.

What carries the argument

Doubly stochastic Poisson process model incorporating Taylor's law for the variance-mean power relationship together with specified temporal correlation decay, from which the closed-form staffing formula is obtained.

If this is right

  • In heavy traffic the dominant determinant of required safety staffing becomes the Taylor's law exponent rather than the mean arrival rate alone.
  • The safety-staffing exponent varies continuously between the square-root value of 1/2 (no over-dispersion) and the linear value of 1 (strong over-dispersion).
  • Service-level targets can be achieved more reliably by using the power-law staffing rule than by applying either the classical square-root or linear rule when arrivals are over-dispersed.
  • The framework supplies a single formula that recovers both classical rules as limiting cases of the same empirical arrival model.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Service systems could estimate the Taylor's law parameter from historical counts and then adjust staffing levels dynamically rather than using a fixed safety rule.
  • The same modeling approach may yield analogous safety-stock formulas for inventory systems whose demand processes obey Taylor's law.
  • Testing the formula on arrival traces from additional industries would reveal how widely the derived exponent range applies.
  • Multi-server queueing models with time-varying rates could incorporate the power-law staffing rule as a building block for optimization.

Load-bearing premise

The arrival process must be representable as a doubly stochastic Poisson process whose variance exactly follows Taylor's law and whose correlations decay in the specific manner required for the closed-form derivation.

What would settle it

Fit the Taylor's law exponent from real arrival counts in disjoint intervals, compute the implied staffing level from the derived formula, and compare the realized fraction of customers served on time against the target; systematic mismatch in heavy traffic would falsify the formula.

read the original abstract

Staffing rules are an essential management tool in service industries for meeting target service levels. The square-root safety rule, based on the Poisson arrival assumption, has been commonly used. However, empirical findings suggest that arrivals often exhibit ``over-dispersion'', meaning that the variance exceeds the mean. In this paper, we develop a new doubly stochastic Poisson process model that captures two key features of over-dispersed arrivals: (i) Taylor's law, which links the variance to the mean through a power-law relationship, and (ii) temporal correlation decay, where the correlation between arrival counts in disjoint time intervals decreases as the time gap grows. Using this model, we study how over-dispersion affects staffing and derive a closed-form staffing formula to ensure a desired service level. Our formula shows that the safety level grows as a power of the nominal load. The exponent lies between 1/2 (the square-root safety rule) and 1 (the linear safety rule). It depends on the degree of over-dispersion, and it implies that Taylor's law is the dominant factor in determining staffing levels in heavy traffic. Extensive numerical experiments with both simulated and real arrival data show that our model and staffing rules significantly outperform various alternatives.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The paper proposes a doubly stochastic Poisson process (DSPP) model for over-dispersed arrivals that enforces Taylor's law (variance-mean power-law scaling) together with a specific form of temporal correlation decay. From this model it derives a closed-form heavy-traffic staffing formula in which the safety staffing level scales as a power of the nominal load, with the exponent lying strictly between 1/2 and 1 and determined by the Taylor's-law over-dispersion parameter. The formula is claimed to unify the classical square-root and linear safety rules, and extensive simulation and real-data experiments are reported to show outperformance relative to standard alternatives.

Significance. If the modeling assumptions hold, the result supplies an explicit, parameter-light bridge between the square-root and linear regimes that is driven by an observable empirical regularity (Taylor's law). The closed-form character and the explicit dependence of the exponent on the over-dispersion degree are genuine strengths; the numerical validation on both simulated and real traces further supports practical relevance in service-system staffing.

major comments (3)
  1. [model definition and heavy-traffic analysis (around the derivation of the staffing formula)] The closed-form staffing expression is obtained only under the joint assumption of exact Taylor's-law marginals and a specific temporal correlation decay of the intensity process that permits an explicit heavy-traffic limit. The manuscript should state this correlation assumption explicitly (likely in the model definition or the proof of the main theorem) and supply either a robustness argument or a counter-example showing what happens to the staffing rule when the correlation structure deviates while the marginal Taylor's law is preserved; without this the claimed unifying formula is conditional on a modeling restriction whose necessity is not yet demonstrated.
  2. [numerical experiments section] The real-data experiments do not isolate whether performance gains survive when the empirical correlation decay differs from the model's required form. A supplementary check that recomputes staffing under the observed correlation structure (or under a deliberately mismatched decay) while keeping the same marginal Taylor's law would directly test the load-bearing modeling assumption.
  3. [parameter estimation and data-analysis subsection] The over-dispersion parameter that enters the exponent is treated as an input taken from the data; the manuscript should clarify the precise estimation procedure (method-of-moments, maximum likelihood, etc.) and whether the same parameter is used both for model fitting and for out-of-sample staffing evaluation, so that readers can judge whether the reported gains are predictive or partly in-sample.
minor comments (2)
  1. [model section] Notation for the intensity process and the correlation kernel should be introduced once and used consistently; several symbols appear to be redefined between the model section and the staffing formula.
  2. [figures] Figure captions for the real-data plots should state the time granularity and the exact service-level target used, to allow direct comparison with the theoretical formula.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The comments highlight important aspects of the modeling assumptions and validation that we will address in a revised manuscript. We respond to each major comment below.

read point-by-point responses
  1. Referee: The closed-form staffing expression is obtained only under the joint assumption of exact Taylor's-law marginals and a specific temporal correlation decay of the intensity process that permits an explicit heavy-traffic limit. The manuscript should state this correlation assumption explicitly (likely in the model definition or the proof of the main theorem) and supply either a robustness argument or a counter-example showing what happens to the staffing rule when the correlation structure deviates while the marginal Taylor's law is preserved; without this the claimed unifying formula is conditional on a modeling restriction whose necessity is not yet demonstrated.

    Authors: We agree that the specific correlation decay structure is essential for obtaining the closed-form heavy-traffic limit. In the revision we will state this assumption explicitly both in the model definition (Section 2) and in the statement of the main theorem. We will also add a short discussion with a counter-example (a long-range dependent intensity process preserving marginal Taylor's law but yielding a different staffing exponent) to illustrate the necessity of the decay assumption. revision: yes

  2. Referee: The real-data experiments do not isolate whether performance gains survive when the empirical correlation decay differs from the model's required form. A supplementary check that recomputes staffing under the observed correlation structure (or under a deliberately mismatched decay) while keeping the same marginal Taylor's law would directly test the load-bearing modeling assumption.

    Authors: We accept this point. The current experiments focus on overall performance but do not isolate the correlation effect. In the revised numerical section we will add a supplementary check that recomputes staffing levels under deliberately mismatched correlation decays (while matching the observed marginal Taylor's law) on both simulated and real traces, to quantify the sensitivity. revision: yes

  3. Referee: The over-dispersion parameter that enters the exponent is treated as an input taken from the data; the manuscript should clarify the precise estimation procedure (method-of-moments, maximum likelihood, etc.) and whether the same parameter is used both for model fitting and for out-of-sample staffing evaluation, so that readers can judge whether the reported gains are predictive or partly in-sample.

    Authors: We will expand the parameter-estimation subsection to specify that a method-of-moments estimator is used, based on regressing log-variance on log-mean across intervals. The same estimated parameter is applied out-of-sample for staffing evaluation; we will add a sentence clarifying this split to confirm the reported gains are predictive. revision: yes

Circularity Check

0 steps flagged

No circularity; staffing exponent derived directly from model parameter

full rationale

The paper defines a doubly stochastic Poisson process whose intensity is constructed to obey Taylor's law (variance-mean power law) plus a specific correlation decay, then derives the closed-form staffing rule as a mathematical consequence of those assumptions. The exponent is an explicit function of the over-dispersion degree supplied as a model input; it is not obtained by fitting to the target quantity or by renaming the input. No self-definitional loops, fitted-input predictions, or load-bearing self-citations appear in the derivation chain. The result is therefore a standard consequence of the stated model rather than a tautology.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on a new modeling assumption (doubly stochastic Poisson process with Taylor's law) and one free parameter (the over-dispersion degree). No new physical entities are postulated.

free parameters (1)
  • over-dispersion degree (Taylor's law exponent)
    The staffing power is a direct function of this quantity, which must be estimated from arrival data.
axioms (1)
  • domain assumption Arrivals follow a doubly stochastic Poisson process whose variance scales as a power of the mean and whose interval correlations decay with time gap.
    This is the modeling premise that enables the closed-form derivation.

pith-pipeline@v0.9.0 · 5763 in / 1487 out tokens · 34141 ms · 2026-05-24T05:28:54.939595+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

73 extracted references · 73 canonical work pages · 1 internal anchor

  1. [1]

    , " * write output.state after.block = add.period write newline

    ENTRY address author booktitle chapter doi edition editor eid howpublished institution isbn issn journal key month note number organization pages publisher school series title type url volume year label extra.label sort.label short.list INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION init.state.consts #0 'before.all := #1...

  2. [2]

    write newline

    " write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max substring 't := if while FUNCTION word.in "" FUNCTION format.date year ...

  3. [3]

    Operations Research 68(2):327--347

    Ata B, Peng X (2020) An optimal callback policy for general arrival processes: A pathwise analysis. Operations Research 68(2):327--347

  4. [4]

    Management Science 50(7):896--908

    Avramidis A, Deslauriers A, L'Ecuyer P (2004) Modeling daily arrivals to a telephone call center. Management Science 50(7):896--908

  5. [5]

    Management Science 56(10):1668--1686

    Bassamboo A, Randhawa RS, Zeevi A (2010) Capacity sizing under parameter uncertainty: Safety staffing principles revisited. Management Science 56(10):1668--1686

  6. [6]

    Operations Research 57(3):714--726

    Bassamboo A, Zeevi A (2009) On a data-driven method for staffing large call centers. Operations Research 57(3):714--726

  7. [7]

    Billingsley P (1999) Convergence of Probability Measures (John Wiley & Sons), 2nd edition

  8. [8]

    Siberian Mathematical Journal 8(5):746--763

    Borovkov AA (1967) On limit laws for service processes in multi-channel systems. Siberian Mathematical Journal 8(5):746--763

  9. [9]

    Operations Research 52(1):17--34

    Borst S, Mandelbaum A, Reiman MI (2004) Dimensioning large call centers. Operations Research 52(1):17--34

  10. [10]

    Brown L, Gans N, Mandelbaum A, Sakov A, Shen H, Zeltyn S, Zhao L (2005) Statistical analysis of a telephone call center: A queueing-science perspective. J. Amer. Statist. Assoc. 100(469):36--50

  11. [11]

    Burnham KP, Anderson DR (2002) Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach (Springer), 2nd edition

  12. [12]

    International Transactions in Operational Research 19(6):771--787

    Channouf N, L'Ecuyer P (2012) A normal copula model for the arrival process in a call center. International Transactions in Operational Research 19(6):771--787

  13. [13]

    Working paper, https://arxiv.org/abs/2311.02577

    Chen X, Hong G (2023) Steady-state analysis and online learning for queues with Hawkes arrivals. Working paper, https://arxiv.org/abs/2311.02577

  14. [14]

    Econometrica 53(2):385--407

    Cox JC, Ingersoll JE, Ross SA (1985) A theory of the term structure of interest rates. Econometrica 53(2):385--407

  15. [15]

    Management Science, forthcoming

    Daw A, Hampshire RC, Pender JJ (2024) How to staff when customers arrive in batches. Management Science, forthcoming

  16. [16]

    Stochastic Systems 8(3):192--229

    Daw A, Pender J (2018) Queues driven by hawkes processes. Stochastic Systems 8(3):192--229

  17. [17]

    Duffie D (2011) Measuring Corporate Default Risk (Oxford University Press)

  18. [18]

    Advances in Physics 57(1):89--142

    Eisler Z, Bartos I, Kert \'e sz J (2008) Fluctuation scaling in complex systems: Taylor's law and beyond. Advances in Physics 57(1):89--142

  19. [19]

    Electroteknikeren 13:5--13

    Erlang AK (1917) Solution of some problems in the theory of probabilities of significance in automatic telephone exchanges. Electroteknikeren 13:5--13

  20. [20]

    Manufacturing & Service Operations Management 5(2):79--141

    Gans N, Koole G, Mandelbaum A (2003) Telephone call centers: Tutorial, review, and research prospects. Manufacturing & Service Operations Management 5(2):79--141

  21. [21]

    Manufacturing & Service Operations Management 17(4):571--588

    Gans N, Shen H, Zhou YP, Korolev N, McCord A, Ristock H (2015) Parametric stochastic programming models for call-center workforce scheduling. Manufacturing & Service Operations Management 17(4):571--588

  22. [22]

    Queueing Systems 90(1):161--206

    Gao X, Zhu L (2018) Functional central limit theorems for stationary Hawkes processes and application to infinite-server queues. Queueing Systems 90(1):161--206

  23. [23]

    Manufacturing & Service Operations Management 4(3):208--227

    Garnet O, Mandelbaum A, Reiman MI (2002) Designing a call center with impatient customers. Manufacturing & Service Operations Management 4(3):208--227

  24. [24]

    Management Science 57(12):2115--2129

    Giesecke K, Kim B, Zhu S (2011) Monte Carlo algorithms for default timing problems. Management Science 57(12):2115--2129

  25. [25]

    Glasserman P (2003) Monte Carlo Methods in Financial Engineering (Springer)

  26. [26]

    Working paper

    Glynn PW, Hong LJ, Zhang X (2019) Modeling call center arrivals: A tale of three timescales. Working paper

  27. [27]

    Operations Research 49(4):549--564

    Green LV, Kolesar PJ, Soares J (2001) Improving the SIPP approach for staffing service systems that have cyclic demands. Operations Research 49(4):549--564

  28. [28]

    Production and Operations Management 16(1):13--39

    Green LV, Kolesar PJ, Whitt W (2007) Coping with time-varying demand when setting staffing requirements for a service system. Production and Operations Management 16(1):13--39

  29. [29]

    Operations Research 29(3):567--588

    Halfin S, Whitt W (1981) Heavy-traffic limits for queues with many exponential servers. Operations Research 29(3):567--588

  30. [30]

    European Journal of Operational Research 296(3):900--913

    Heemskerk M, Mandjes M, Mathijsen B (2022) Staffing for many-server systems facing non-standard arrival processes. European Journal of Operational Research 296(3):900--913

  31. [31]

    Fundamental Research 3(4):627--639

    Hong LJ, Liu G, Luo J, Xie J (2023) Variability scaling and capacity planning in Covid -19 pandemic. Fundamental Research 3(4):627--639

  32. [32]

    Management Science 71(3):2079--2126

    Hu Y, Chan CW, Dong J (2025) Prediction-driven surge planning with application to emergency department nurse staffing. Management Science 71(3):2079--2126

  33. [33]

    International Journal of Forecasting 32(3):865--874

    Ibrahim R, Ye H, L'Ecuyer P, Shen H (2016) Modeling and forecasting call center arrivals: A literature survey and a case study. International Journal of Forecasting 32(3):865--874

  34. [34]

    Journal of Applied Probability 2(2):429--441

    Iglehart DL (1965) Limit diffusion approximations for the many-server queue and the repairman problem. Journal of Applied Probability 2(2):429--441

  35. [35]

    Management Science 42(10):1383--1394

    Jennings OB, Mandelbaum A, Massey WA, Whitt W (1996) Server staffing to meet time-varying demand. Management Science 42(10):1383--1394

  36. [36]

    Applied Stochastic Models in Business and Industry 17:307--318

    Jongbloed G, Koole G (2001) Managing uncertainty in call centers using poisson mixtures. Applied Stochastic Models in Business and Industry 17:307--318

  37. [37]

    Karlin S, Taylor HM (1981) A Second Course in Stochastic Processes (Academic Press)

  38. [38]

    Production and Operations Management 24(7):1101--1117

    Ko c a g a YL, Armony M, Ward AR (2015) Staffing call centers with uncertain arrival rates and co-sourcing. Production and Operations Management 24(7):1101--1117

  39. [39]

    Production and Operations Management 7(3):282--293

    Kolesar PJ, Green LV (1998) Insights on service system design from a normal approximation to erlang's delay formula. Production and Operations Management 7(3):282--293

  40. [40]

    Annals of Probability 19(3):1035--1070

    Kurtz TG, Protter P (1991) Weak limit theorems for stochastic integrals and stochastic differential equations. Annals of Probability 19(3):1035--1070

  41. [41]

    Lamberton D, Lapeyre B (2007) Introduction to Stochastic Calculus Applied to Finance (Chapman and Hall/CRC), 2nd edition

  42. [42]

    Operations Research 60(6):1551--1564

    Liu Y, Whitt W (2012) Stabilizing customer abandonment in many-server queues with time-varying arrivals. Operations Research 60(6):1551--1564

  43. [43]

    Master's thesis, Technion -- Israel Institute of Technology

    Maman S (2009) Uncertainty in the Demand for Service: The Case of Call Centers and Emergency Departments. Master's thesis, Technion -- Israel Institute of Technology

  44. [44]

    Operations Research 57(5):1189--1205

    Mandelbaum A, Zeltyn S (2009) Staffing many-server queues with impatient customers: Constraint satisfaction in call centers. Operations Research 57(5):1189--1205

  45. [45]

    Advances in Applied Probability 25:518--548

    Meyn SP, Tweedie RL (1993) Stability of Markovian processes III : Foster-Lyapunov criteria for continuous-time processes. Advances in Applied Probability 25:518--548

  46. [46]

    ksendal B (2003) Stochastic Differential Equations: An Introduction with Applications (Springer), 6th edition

  47. [47]

    Operations Research 64(2):510--527

    Oreshkin BN, R \'e egnard N, L'Ecuyer P (2016) Rate-based daily arrival process models with application to call centers. Operations Research 64(2):510--527

  48. [48]

    Management Science 61(1):73--91

    Pang G, Perry O (2015) A logarithmic safety staffing rule for contact centers with call blending. Management Science 61(1):73--91

  49. [49]

    Probability Surveys 4:193--267

    Pang G, Talreja R, Whitt W (2007) Martingale proofs of many-server heavy-traffic limits for M arkovian queues. Probability Surveys 4:193--267

  50. [50]

    Sociological Methodology 25:111--163

    Raftery AE (1995) Bayesian model selection in social research. Sociological Methodology 25:111--163

  51. [51]

    Applied Stochastic Models in Business and Industry 22(3):297--311

    Shen H, Brown L (2006) Non-parametric modelling of time-varying customer service times at a bank call centre. Applied Stochastic Models in Business and Industry 22(3):297--311

  52. [52]

    Annals of Applied Statistics 2:601--623

    Shen H, Huang J (2008) Forecasting time series of inhomogeneous Poisson process with application to call center workforce management. Annals of Applied Statistics 2:601--623

  53. [53]

    Spall JC (2003) Introduction to Stochastic Search and Optimization (Wiley-Interscience)

  54. [54]

    Steele JM (2001) Stochastic Calculus and Financial Applications (Springer)

  55. [55]

    Anesthesiology 92(4):1160--1167

    Strum DP, May JH, Vargas LG (2000) Modeling the uncertainty of surgical procedure times: Comparison of the log-normal and normal models. Anesthesiology 92(4):1160--1167

  56. [56]

    Naval Research Logistics 68(3):312--326

    Sun X, Liu Y (2021) Staffing many-server queues with autoregressive inputs. Naval Research Logistics 68(3):312--326

  57. [57]

    Nature 189(4766):732--735

    Taylor LR (1961) Aggregation, variance and the mean. Nature 189(4766):732--735

  58. [58]

    Taylor RAJ (2019) Taylor’s Power Law: Order and Pattern in Nature (Academic Press)

  59. [59]

    Advances in Applied Probability 14(1):171--190

    Whitt W (1982) On the heavy-traffic limit theorem for GI/G/ queues. Advances in Applied Probability 14(1):171--190

  60. [60]

    Management Science 38(5):708--723

    Whitt W (1992) Understanding the efficiency of multi-server service systems. Management Science 38(5):708--723

  61. [61]

    Operations Research Letter 24:205--212

    Whitt W (1999) Dynamic staffing in a telephone call center aiming to immediately answer all calls. Operations Research Letter 24:205--212

  62. [62]

    Whitt W (2002) Stochastic-Process Limits (Springer)

  63. [63]

    Production and Operations Management 15(1):88--102

    Whitt W (2006) Staffing a call center with uncertain arrival rate and absenteeism. Production and Operations Management 15(1):88--102

  64. [64]

    Probability Surveys 4:268--302

    Whitt W (2007) Proofs of the martingale FCLT . Probability Surveys 4:268--302

  65. [65]

    Proceedings of the 2013 Winter Simulation Conference, 713--723

    Zhang X (2013) A Bayesian approach for modeling and analysis of call center arrivals. Proceedings of the 2013 Winter Simulation Conference, 713--723

  66. [66]

    Affine Jump-Diffusions: Stochastic Stability and Limit Theorems

    Zhang X, Glynn PW (2018) Affine jump-diffusions: Stochastic stability and limit theorems. Working paper, https://arxiv.org/abs/1811.00122

  67. [67]

    Management Science 56(10):1668--1686

    Bassamboo A, Ramandeep RS, Zeevi A (2010) Capacity sizing under parameter uncertainty: Safety staffing principles revisited. Management Science 56(10):1668--1686

  68. [68]

    Borovkov AA (1984) Asymptotic Methods in Queueing Theory (John Wiley & Sons)

  69. [69]

    Green LV Green, Kolesar PJ, Whitt W (2007) Coping with Time-Varying Demand When Setting Staffing Requirements for a Service System Production and Operations Management 16(1):13--39

  70. [70]

    Karatzas I, Shreve SE (1991) Brownian Motion and Stochastic Calculus (Springer), 2nd edition

  71. [71]

    Probability Surveys 4:193--267

    Pang G, Talreja R, Whitt W (2007) Martingale proofs of many-server heavy-traffic limits for Markovian queues. Probability Surveys 4:193--267

  72. [72]

    Operations Research 24(4):808--823

    Segal M (1974) The operator scheduling problem: A network-flow approach. Operations Research 24(4):808--823

  73. [73]

    Probability Surveys 4:268--302

    Whitt W (2007) Proofs of the martingale FCLT. Probability Surveys 4:268--302