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    Holt, Modigliani, Muth, and Simons work and its role in therenaissance and evolution of operations management

    Jaya Singhal, Kalyan Singhal *

    Merrick School of Business, University of Baltimore, 1420 N. Charles Street, Baltimore, MD 21201, USA

    Available online 17 July 2006

    Abstract

    Early work in aggregate production planning has evolved into a major business process known as sales and operations planning.

    In the 1950s, a team led by Holt, Modigliani, Muth, and Simon, which also included Bonini and Winters, worked on aggregate

    production planning and forecasting and published a series of papers and a book. The literature contains reports of at least 73

    applications of their work in four companies and three application studies. Holt et al.s work and its visibility led to a renaissance of

    the field of operations and supply chain management as we know it today and brought two paradigm changes in the domain and the

    role of operations and supply chain management. First, seemingly unrelated and non-managerial individual functions started to

    emerge as parts of an integrated system of managing production. Second, aggregate production planning brought to forefront the

    central role of operations management by linking it with supply chains and other functions in the organization.

    # 2006 Elsevier B.V. All rights reserved.

    Keywords: Aggregate planning; Capacity management; Evolution of operations management; Interdisciplinary; Manufacturing planning and

    control; Sales and operations planning

    1. Introduction: the genesis of Holt, Modigliani,

    Muth, and Simons work

    In the early 1950s, Charles C. Holt, Franco

    Modigliani, John F. Muth, and Herbert A. Simon

    (HMMS) began work on a project, Planning and

    Control of Industrial Operations, at the Graduate

    School of Industrial Administration (GSIA) at the

    Carnegie Institute of Technology. William W. Cooper,

    who was also at GSIA, initiated the project, and the

    Office of Naval Research supported it. Our goal in this

    paper is to document the early work of HMMS in

    aggregate production planning and to describe how this

    work has evolved into a major business process known

    as sales and operations planning.

    Holt had four degrees in electrical engineering and

    economics from MITand the University of Chicago, and

    he wanted to study how instability in the economy was

    related to firms management of their inventories.

    Modigliani (awarded the Nobel Prize in 1985) received

    a J.D. in 1939 from the University of Rome and a D.S.S.

    in 1944 from the New School of Social Research. He had

    worked on production smoothing. Simon (awarded the

    Nobel Prize in 1978) received his Ph.D. from the

    University of Chicago in 1943. A cognitive scientist,

    economist, organizational theorist, and political scientist,

    he had worked on the dynamics of inventory feedback

    on production rates. He was interested in understanding

    how managers made their decisions, and he wanted to

    model their behavior. Muth had an undergraduate degree

    in industrial engineering and was a graduate student at

    the GSIA where he earned a Ph.D. in 1962. He published

    a paper on rational expectations in 1961, derived from

    www.elsevier.com/locate/jomJournal of Operations Management 25 (2007) 300309

    * Corresponding author. Tel.: +1 410 837 4976.

    E-mail address:[email protected](K. Singhal).

    0272-6963/$ see front matter # 2006 Elsevier B.V. All rights reserved.

    doi:10.1016/j.jom.2006.06.003

    mailto:[email protected]://dx.doi.org/10.1016/j.jom.2006.06.003http://dx.doi.org/10.1016/j.jom.2006.06.003mailto:[email protected]
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    the work on the project, Planning and Control of

    Industrial Operations. Robert Lucas built on Muths

    work and won a Nobel Prize in 1995.

    According toSimon (1978a), the goal of the GSIA,

    which was newly established in 1949, was to place

    business education on a foundation of fundamental

    studies in economics and behavioral science. Simonnoted that the work on the HMMS project was a part of

    this effort, and that fortunately the computer and the

    new management science techniques had just started

    appearing.

    1.1. Production management just before the HMMS

    work

    Commenting on the state of operations and supply

    chain management in the early 1950s, Muth (2004a)

    noted, Textbooks at the time focused on the EOQformula, Gantt chart displays, punched card systems for

    dispatching, moving average forecasts, and thats about

    it. In the textbook,Analysis of Production Management,

    Bowman and Fetter (1957)(then assistant professors at

    MIT) essentially covered hypothesis testing, various

    charts (Gantt charts, activity charts, and so forth),

    mathematical programming, statistical control, sampling

    inspection, industrial experimentation, total value ana-

    lysis, Monte Carlo analysis, and equipment investment

    analysis.Holt (2002)said that a few years before they

    started work on the project, a consulting firm had sold Asimple lot size formula to Westinghouse Electrical

    Corporation for something like $100,000. It presum-

    ably included the consultants time. The HMMS work

    was a turning point in the direction of operations

    management.

    2. The HMMS model and its solution

    The HMMS team started the project by interviewing

    managers at about 15 companies. According to Holt

    (2002), the managers initially denied that they had any

    problems, but after persistent questioning, the teamfound that the managers were simply going from one

    crisis to another: inadequate forecasts of wildly

    fluctuating demand for thousands of products, huge

    fluctuations between overtime and idle time, and gross

    incompatibilities between aggregate production plans

    and plans for individual products.

    The team finally focused on an application

    oriented context (Cooper, 2004) for scheduling paint

    production at the Springdale plant of the Pittsburgh

    Glass Corporation (now PPG Industries) because it

    had the generic system problem in a fairly simple

    form. Augier and March (2004) observed that the

    project was essentially a study of decision making under

    uncertainty.

    2.1. The HMMS model

    The core of HMMS work was a linear-quadraticmodel of aggregate production planning. HMMS

    submitted an article based on their findings to

    Operations Research, which rejected it on the basis

    that the work was not operations research (Cooper,

    2004). HMMS then published their findings in two

    papers in the second volume ofManagement Science

    (Holt et al., 1955, 1956). Several other papers

    concerning the Planning and Control of Industrial

    Operations project accompanied these two, for

    example, Simon (1955, 1956), Bonini (1958), Muth

    (1960), and Winters (1960). Holt et al. (1960) thenpublished a book that covered these papers and the two

    in Management Science. Bonini and Winters, Ph.D.

    students at GSIA at the time, also contributed to the

    book. Several other papers on parts of the project and

    some derived from it followed (Muth, 1961; Holt and

    Modigliani, 1961; Holt, 1962; Winters, 1962).

    The Holt et al. model (1960) consists of selecting

    production and workforce levels in each ofTperiods so

    as to satisfy ordered shipments while minimizing the

    sum of the costs over theTperiods. LetPt,Wt,It, andSt

    represent production volume, workforce level, end-of-period inventory, and ordered shipment for periodt, and

    letI0and W0represent the specified values of the initial

    inventory and the initial workforce. The cost in periodt

    consists of the following components:

    Regular payroll costs : C1Wt C13

    Hiring and layoff costs : C2Wt Wt1 C112

    Overtime costs :

    C3Pt

    C4W

    t

    2

    C

    5Pt

    C6W

    tC

    12PtW

    t

    Inventory-related costs : C7It C8 C9St2

    The model was thus formulated as

    ZXT

    t1

    C13 C1 C6Wt

    C2Wt Wt1 C112 C3Pt C4Wt

    2

    C5Pt C12PtWt C7It C8 C9St2

    (1)

    J. Singhal, K. Singhal / Journal of Operations Management 25 (2007) 300309 301

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    Subject to

    Pt St It It1 (2)

    C1, C2, . . ., C12 are constants. Holt et al. used curve

    fitting to estimate the values of cost coefficients.

    2.2. A solution of the model

    Holt et al. (1960, pp. 9495)derived the following

    recursive equations to solve the model:

    PtC10

    C14 C15Wt1 C17Wt C15Wt1 (3)

    It C3

    C7Pt1 Pt

    C14

    2C7Wt1 Wt C8 C9St

    (4)

    where t= 1, 2, . . ., (T1); C10= C1C6;C14= 2C3C4C12; C15= 2C2/C14; C16 2C3C24=C14;C17= C16+ 2C15.

    Holt et al. focused on an infinite planning horizon

    with stationery costs. Modigliani and Muth constructed

    efficient computational algorithms. Holt and Simon

    derived the rules for optimal decisions under certainty.

    Via a series of tedious linear transformations, they

    derived the following two linear decision rules (LDRs)

    for the first period:

    P1 u1 u2I0u3W0XT

    t1

    tSt

    W1 u4 u5I0u6W0XT

    t1

    mtSt

    whereu1,u2,u3,u4,u5,u6,wt, andmt(t= 1, 2, . . .,T) are

    functions of the cost coefficients. The infinite series can

    be truncated after an appropriate number (T) of periods.

    Bonini (1958) describes a method for disaggregating the

    aggregate plan to determine production levels for indi-

    vidual products. For more recent alternate approaches to

    solving the Holt et al. model, see Singhal (1992)and

    Singhal and Singhal (1996).

    2.3. Certainty-equivalence

    Simon (1956)proved a certainty-equivalence theo-

    rem so that the Holt et al. model could also be applied

    under conditions of uncertainty. In his Nobel memorial

    lecture, Simon (1978b) pointed out that under

    uncertainty about future sales, only the expected values,

    and not higher moments, of the probability distributions

    enter into the decision rule. Recently, Muth (2004b) said

    that the results of the theorem were important because

    they showed that the LDRs were appropriate for a

    quadratic criterion function under uncertainty and that

    the expected value was a sufficient statistic. Muth added

    that linear programming or other techniques did not

    share this property. Holt (2002) noted that Simon

    proved that the solution of this model was optimal

    both statically and dynamically, and that the theoremwas a powerful tool for dealing with large dynamic

    systems under uncertainty.

    Holt et al. (1960, p. 123)noted the following specific

    implications of the certainty-equivalence theorem for

    the linear quadratic model: When costs are quadratic,

    the only datum about future sales that enters into the

    optimal decision rule is the expected value; that is, an

    average estimate of what the sales for each relevant

    future time period are likely to be. The probable

    dispersion of actual future sales around this predicted

    average and the finer characteristics of the probabilitydistribution of sales are irrelevant. The procedure

    involves using a sales forecasting method that does not

    consistently overestimate or underestimate sales. In

    other words (Holt et al., 1956, p. 176), A forecasting

    method should be used whose expected error is zero, or

    more loosely, whose algebraic average error is zero.

    3. Industrial applications of the HMMS model

    Holt et al. (1960, pp. 1536)reported 73 applications

    in four companies: 70 factories of Pittsburgh GlassCorporation, Westinghouse Electrical Corporation (a

    manufacturer of electrical products), a company in a

    process industry, and a manufacturer of cooking

    utensils. They also reported two application studies,

    for a fiber company and for an ice cream company.Lee

    and Khumawala (1974) also reported an application

    study in the capital goods industry. We summarize these

    applications.

    3.1. Seventy factories of Pittsburgh Glass

    Corporation (now PPG industries)

    The factory, where the model was originally tested

    (nicknamed as Paint Factory in Holt et al.s publica-

    tions), had nearly 1000 products. The implementation

    originally covered only 10% of the sales volume of the

    factory. With encouraging results in reducing back

    orders, inventory levels, and fluctuations in aggregate

    production, the factory first extended the model to cover

    25% of the sales volume and then gradually to 100%.

    Holt (2002)noted, after the new methods for the paint

    company applications were fully developed and tested,

    the paint company had difficulty in achieving a profit

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    impacting payoff. That problem was ultimately solved,

    and the system extended to all 70 of the paint companys

    factories. But that did not occur until a few years later,

    when a new quantitatively oriented manager was given

    specific responsibility for implementing the new

    system.

    Muth (2004b) noted, It was discovered that thefactory demand fluctuations were generated by the

    companys own distribution system. Final demand

    was fairly flat. This led to something like distribution

    requirements planning for the production schedule.

    The factory demand fluctuations clearly appear to

    have resulted from the bullwhip effect.Gordon (1966)

    also reported on the state of implementation at the

    original paint factory several years after the initial

    study. According to him, the foremen were using the

    results of the decision rules only if the rules agreed

    with their judgment; otherwise they went by theirjudgment and did so in half of the cases. The

    management meanwhile believed that the rules were

    being used except in the odd case when judgment

    indicated that they should be overruled. Gordon

    further reported that at a later date, the company

    centralized the calculations of decision rules. Then at

    some point, the finished goods inventory increased

    to alarming levels. An investigation showed that

    the decision rules for reducing the workforce were

    not followed because it was against the company

    policy to lay off workers. Gordon noted, This meantthat each period the work force rule was indicating a

    reduction in the work force; the production rule,

    attempting to minimize costs given the present work

    force level but anticipating layoff, called for some

    production for the excess work force. The rules

    were interactive, but in this case the interaction had

    been eliminated.

    3.2. Other applications

    3.2.1. Westinghouse Electrical Corporation (an

    electrical manufacturer)One of Westinghouses factories supplied about 500

    different models of transformers to 30 warehouses.

    Operations research specialists and the personnel of the

    transformer department jointly developed a mathema-

    tical model of the system. The model was similar to the

    one used for the paint factory. For 3 months, the new and

    old systems operated in parallel. The benefits included

    fewer stock-outs, a reduction of 20 percent (or about $

    three million in 1960 money) in inventory, improved

    service to warehouses as reflected in a 50% reduction in

    long distance calls that were normally service related,

    and facilitation of design changes since the system

    could control the inventory of both the old and the new

    products.

    3.2.2. A company in a process industry

    In the process company, the decision rules of the

    HMMS model determined the aggregate production andworkforce levels. The analysts revised the rules based

    on managers judgment, and the company used its

    customary method to allocate production to indivi-

    dual products. The decision rules required smaller

    changes in the workforce than the traditional method.

    The managers, however, produced more than the rules

    recommended, but when the inventory started to build

    up, their confidence in the decision rules increased.

    3.2.3. A manufacturer of cooking utensils

    The manufacturer produced approximately 1000products. The sales department made higher forecasts

    than those made by the production department, and the

    conflict led to fluctuations in production and employ-

    ment. Their joint participation in the HMMS study led

    to greater agreement on the desirable levels of

    inventory. The system developed for this company

    had an additional feature (Holt et al., 1960, p. 33):

    When the inventory of a product fell low enough, a

    new production lot was triggered. If the distribution of a

    product among the warehouses had remained in

    balance, the total inventory level was allowed to falllower than if the distribution became unbalanced and

    one or several warehouses were in danger of stock-

    outs. Winters (1958) described this trigger. A

    simulation study with different stock-out costs showed

    that the company could reduce warehouse inventory by

    40% while decreasing stock-outs. These results

    encouraged the company to try the new system for a

    sample of 26 representative products.

    3.2.4. A fiber manufacturer

    For a fiber manufacturer, the linear decision rule

    gave decisions that were no better than thosepreviously made by management (Holt et al., 1960,

    p. 34) because with large jumps in the workforce and

    production level, the quadratic cost functions were not a

    good fit.

    3.2.5. An ice cream plant

    van der Velde (1958) worked on applying the Holt

    et al. model at an ice cream plant as a part of his

    Masters Thesis at MITunder the supervision of Edward

    H. Bowman. During a 2-year study period, the LDRs led

    to savings of the order of one percent.Holt et al. (1960)

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    compared this study with that for the original paint

    factory and noted that although the performances of

    the decision rules were somewhat similar in the two

    cases, the respective rules depended upon the cost

    functions (Holt et al., 1960, p. 36). As an example, Holt

    et al. pointed out that a company would have small

    inventory fluctuations if the costs of inventory fluctua-tions were high, and vice versa.

    3.2.6. A factory in the capital goods industry

    The capital goods factory was a job-shop manu-

    facturing facility, and the study was done with the

    cooperation and encouragement of its management.

    The factory assembled finished goods for inventory and

    to fill customer orders, and manufactured parts for

    inventory. Lee and Khumawala (1974) developed a

    corporate simulation model that closely followed the

    accounting system and the material flow through theorganization. They evaluated four models, including the

    Holt et al. model. They found that with imperfect

    forecasts, application of the Holt et al. model would

    have increased the factorys annual profits by more than

    nine percent to $ 4,821,000 compared to its actual profit

    of $ 4,420,000.

    4. The role of HMMS work in renaissance of

    operations management and of business

    education

    4.1. Production as the core of economics

    The production of goods and services has been the

    core of all economic activities since the dawn of

    civilization. It remained the core of the field of

    economics as modern economics developed with the

    Industrial Revolution and with the works of Adam

    Smith (17231790) published in 1776, of Thomas R.

    Malthus (17661834) published in 1798, of David

    Ricardo (17721823) published in 1817, and of Karl

    Marx (18181883) published in 1848, 1867, 1885, and

    1894. However, since the beginning of the 20th century,many new issues related to manufacturing surfaced.

    They were distinct from mainstream economics and

    constituted an emerging field called production man-

    agement.

    4.2. A renaissance

    Holt et al.s work and its visibility led to a renaissance

    of the field of operations management, as we know it

    today. The issues of aggregate production planning and

    disaggregation that Holt et al. addressed represent the

    primarylinks between strategic andtactical decisions in a

    firm. Aggregate production planning links operations

    with strategy. It plays a key role in enterprise resource

    planning and organizational integration by linking

    operations with accounting, distribution, finance, human

    resource management, and marketing. It also drives

    interorganizational coordination by linking operationswith both upstream and downstream supply chains. It has

    several specific roles:

    Aggregate production planning serves as a majorvehicle for implementing manufacturing strategy

    because it concerns trade-offs between cost, flex-

    ibility, and delivery time.

    It serves as an input to, and is constrained by, long-range capacity planning. Therefore, it plays a role in

    investments in physical facilities.

    It is a mechanism for implementing supply chainstrategy since it mitigates the impact of the bullwhip

    effect and determines product mix, material require-

    ments, levels of procurement, the flow of products in

    the downstream supply chain, and the timing of order

    fulfillment.

    It is the primary vehicle for coordinating multiplantoperations.

    It determines the levels of accounts receivable andaccounts payable and also the short-term to medium-

    term requirements for cash to support operations and

    inventory. It sets the levels of employment, the number of shifts,and the utilization of the workforce.

    The renaissance brought two paradigm changes in

    the domain and the role of operations and supply chain

    management. First, what had seemed unrelated and

    non-managerial individual functions, such as hypoth-

    esis testing, industrial engineering and quantitative

    tools, statistical quality control, sampling inspection

    and industrial experimentation, value analysis, and

    equipment-investment analysis, started to emerge as

    parts of an integrated system of managing production.Second, the focus on the issues related to aggregate

    production planning brought to forefront the central role

    of operations management in linking other functions,

    such as accounting, finance, human resource manage-

    ment, information systems, marketing, and strategy.

    Commenting on the interdisciplinary nature of

    aggregate production planning, (Silver, 1972, p. 15),

    observed, The production supervisor desires long runs

    of individual items so as to reduce production costs; the

    marketing personnel wish to have a substantial inventory

    of a wide range of finished goods; those concerned with

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    labor relations desire a stable work force; finally, the

    comptroller generally wants as low inventory as possible.

    . . .Therefore, a cross-departmental (or systems) appro-

    ach to the solution of the problem is essential.

    The renaissance in operations management paral-

    leled other changes in business schools. Geoffrion

    (2003) pointed out, The emergence of modernbusiness schools dates from about 1959, when the

    Carnegie and Ford foundations issued separate reports

    lamenting the lack of rigor and research in US business

    schools. The developments at the GSIA at the

    Carnegie Institute of Technology during the 1950s

    had a major influence on the two reports. Thus, Holt

    et al.s work also played a role in renaissance of business

    education as we know it today.

    4.3. A standard of excellence to judge our current

    research

    Sprague et al. (1990) used Holt et al.s work as an

    exemplar in reviewing the research on production

    planning, inventory management, and scheduling, and

    they observed, The translation of demand for a product

    into load on operational resources constitutes a critical

    problem that is never solved. The astute manager seeks

    a process by which the ever present problem can be

    solved, rather than a specific solution (p. 297). They

    suggested that the HMMS problem definition and

    methodology of attack were exemplary models ofour research questions and attempted to find

    solutions to the problems of practicing managers,

    and that the vocabulary and research methodology

    HMMS developed were seminal and remain a

    standard of excellence by which current research

    could be judged.

    5. Alternate approaches to aggregate production

    planning

    Bowman (1963) used regression analysis on man-

    agers past performance to develop decision rules foraggregate planning. Bowmans work had an impact far

    beyond operations management, particularly in artifi-

    cial intelligence, but a detailed discussion is beyond the

    scope of our paper. Jones (1967) developed two

    heuristic rules, one for size of workforce and another

    for production rate, and tested both his model and the

    HMMS model using the Harvard Business Schools

    Management Simulation Game. Taubert (1968) con-

    verted the HMMS model into a 20-dimension response

    surface and used a search decision rule to find the

    solution. His model eliminated all restrictions imposed

    by linear or quadratic cost models.Lee and Khumawala

    (1974) studied a factory in the capital goods industry

    and used simulation to compare the HMMS model with

    the Bowmans, Jones, and Tauberts models. They

    found that all four models performed credibly with

    perfect forecasts and that the Taubert and HMMS

    models provided the best results. They further foundthat, with imperfect forecasts, the Taubert model

    performed the best, closely followed by the Jones,

    HMMS, and Bowman models.

    Hax and his colleagues (Hax and Meal, 1975; Bitran

    and Hax, 1977; Bitran et al., 1981, 1982) developed

    hierarchical production-planning systems. Hax and

    Candea (1984, p. 393)noted, Early motivation for this

    approach can be found in the pioneering work of Holt,

    Modigliani, Muth, and Simon. Hax and his colleagues

    grouped production management decisions in three

    broad categories (Hax and Candea, 1984, p. 393):

    Policy formulations, capital investment decisions, anddesign of physical facilities.

    Aggregate production planning.Detailed production scheduling.

    Hax and Candea (1984, p. 393)suggested that these

    three categories of decisions differ markedly in terms

    of level of management responsibility and interaction,

    scope of the decision, level of detail of the required

    information, length of the planning horizon needed toassess the consequences of each decision, and degree of

    uncertainties and risks inherent in each decision.Hax

    and Meal (1975) noted, It is only natural, therefore,

    that a system designed to support the overall planning

    process should correspond to the hierarchical structure

    of the organization. Bradley et al. (1977) described

    two real-world applications of hierarchical production

    planning, one in the continuous manufacturing process

    in the aluminum industry (Chapter 6) and another in a

    naval job shop (Chapter 10). Ritzman et al. (1979)

    described related works.

    The developments during the last 50 years havemade it easier and simpler to plan aggregate production.

    The authors of current textbooks describe the use of

    spreadsheets and optimization done with the Excel

    Solver.

    6. Conclusions: where we are now

    The problem Holt, Modigliani, Muth, and Simon

    addressed is now viewed in practice as sales and

    operations planning. It plays a pivotal role in integrating

    the operations, marketing, and finance functions.

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    Duringthe last 50 years, the integrationof these functions

    has been greatly facilitated by the availability of

    optimization software and enterprise resource planning

    systems and the advent of the Internet. It has made a

    profound impact on the evolution of operations and

    supply chain management and yield (revenue) manage-

    ment. The scope of integration now also includes suchissues as detailed scheduling (Dawande et al., 2006),

    delivery guarantees (Rao et al., 2005; Boyaci and Ray,

    2006), interorganizational coordination (Buhman et al.,

    2005; Ferguson and Ketzenberg, 2006; Majumdar and

    Ashok Srinivasan, 2006), manufacturing flexibility stra-

    tegies (Ketokivi, 2006), and the role of pricing. The

    evolving role of integration on a range of topics has been

    widely covered in the literature. Five review papers

    (Boyer et al., 2005; Kleindorfer et al., 2005; Kouvelis

    et al., 2005; Krishnan and Loch, 2005; Schroeder et al.,

    2005) describe a number of papers that address variousdimensions of integration.

    Lee and Ng (1997) pointed out that the interdisci-

    plinary perspective, combined with the benefits of

    interorganizational coordination, has been primarily

    responsible for the new paradigm in supply chain

    management and for the tremendous excitement and

    top management attention on this subject. They noted,

    It seems that the distinction between the so-called

    supply chain management today and traditional opera-

    tions management lies in two dimensions of integration

    and coordination: organizational integration and flowcoordination. . . .Companies are also overcoming the

    functional boundaries, so that the different disciplines

    and functions, such as manufacturing, distribution,

    marketing, accounting, information, and engineering,

    are better integrated.

    In the rapidly growing area of yield and revenue

    management, the models for matching short-term

    supply and demand have become a fundamental

    component of the daily operations of manufacturing

    and service companies because managers can effec-

    tively manipulate price to encourage or discourage

    demand in the short run (Bitran and Caldentey, 2003).Geoffrion (2002)pointed out that the digital economy

    was facilitating dynamic pricing (better and faster

    changes in posted prices in response to market

    conditions, costs, demand, inventory, and competitors

    behavior and better price discrimination through better

    real-time segmentation) and added, This seems to be a

    point of convergence of Marketing and Operations

    Management as management disciplines. Pricing is

    becoming less like a class of decisions made

    episodically by marketing specialists and more like

    an operational process in which pricing decisions are

    dynamically integrated with the traditional steps of the

    online sales process and also with operating data and

    decisions that have been traditional OM concerns. The

    applications of models in industry have also been

    driving academic research (Gallego and Van Ryzin,

    1997; Baker and Collier, 2003).

    The integrated approach to planning is becomingmore and more a standard practice in companies. It is

    also facilitating and is being facilitated by globalization

    and the emergence of distributed supply chains. Holt,

    Modigliani, Muth, and Simon were clearly way ahead

    of their time in understanding the importance of this

    integrated approach to planning.

    Acknowledgements

    We are grateful to Charles Holt and Jack Muth for

    sharing a number of ideas with us. We also thank LindaSprague for several useful suggestions.

    Appendix A. Biographies of Holt, Modigliani,

    Muth, and Simon

    A.1. Charles C. Holt (1921till date)

    Charles Holt is professor emeritus at the Red

    McCombs School of Business of the University of

    Texas at Austin. He earned his B.S. and M.S. degrees in

    electrical engineering from MIT and M.A. and Ph.D.(1955) in economics from the University of Chicago. He

    has held positions at the MIT Servo Lab, the Carnegie

    Institute of Technology, the London School of Econom-

    ics, the University of Wisconsin, and the Urban Institute.

    Holts research concerns a wide range of topics,

    including automatic control, computer simulation,

    control theory, decision support systems for unstruc-

    tured problems, macroeconomic theory, and operations

    research. He worked with Winters to develop the Holt

    Winters exponential smoothing models of forecasting

    that are widely used in business forecasting. They are

    embedded in almost all forecasting software and taughtin almost all business programs.

    Holt led the Holt, Modigliani, Muth, and Simon

    team. In a 2002 article in Operations Research, he

    observed, Looking back all members of the team

    would likely agree that their GSIA years were among

    the most interesting and exciting of their careers.

    A.2. Franco Modigliani (19182003)

    Franco Modigliani was born in Rome, Italy. He was

    educated at the Sorbonne and the University of Rome,

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    where he earned a Doctor Juris degree in 1939. The

    same year, he moved to the United States and joined the

    New School for Social Research. One of his mentors

    there was Jacob Marschak who later worked with

    Kenneth Arrow and Theodore Harris to lay the

    foundations of inventory theory under uncertainty.

    Modigliani earned his D.S.S. there in 1944 and taughtthere from 1944 to 1949. He was a research consultant

    to the Cowles Commission at the University of Chicago

    from 1949 to 1952.

    Modigliani moved to the Carnegie Institute of

    Technology in 1952 where he collaborated with

    Charles Holt, John Muth, and Herbert Simon on

    production smoothing and with Merton Miller on the

    effect of financial structure and dividend policy on

    the market value of a firm. During this period, he

    also worked with Richard Brumberg, a Ph.D. student

    at John Hopkins University, to lay the foundations ofwhat later became the life cycle hypothesis of saving.

    In 1960, he moved to MIT where he remained for the

    rest of his career.

    Modigliani was awarded the Nobel Prize in

    economics in 1985 for his pioneering analyses of

    savings and financial markets. He also served as

    president of the International Economic Association,

    the Econometric Society, the American Economic

    Association, and the American Finance Association.

    A.3. John F. Muth (19302005)

    John Muth had an undergraduate degree in industrial

    engineering, and he earned his Ph.D. from the Graduate

    School of Industrial Administration at the Carnegie

    Institute of Technology in 1962. He was a visiting

    lecturer at the University of Chicago in 19571958, and

    he spent 19611962 at the Cowles Foundation at Yale

    University. He was a research associate (19561959), an

    assistant professor (19591962), and an associate

    professor (19621964) at the Carnegie Institute of

    Technology. He served on the faculty of Michigan State

    University from 1964 to 1969 and on the faculty ofIndiana University from 1969 until his retirement in

    1994.

    Muth made notable contributions to learning theory

    and was one of the first to study artificial intelligence.

    While still a Ph.D. student, he published Rational

    expectations and the theory of price movements in

    1961. Robert Lucas built on Muths work and won a

    Nobel Prize in 1995. Muth is known as the father of

    rational expectation theory, which changed almost

    every area of economic research. Economist Ike

    Branon wrote, While he (Muth) would have appre-

    ciated the recognition of a Nobel Prize, Muth was a shy

    gentleman who would have been uncomfortable with

    the notoriety that comes with the prize. He was much

    more at home at the various pubs in downtown

    Bloomington, where he was not averse to holding his

    office hours. [http://www.cato.org/pub_display.php?-

    pub_id=5362].

    A.4. Herbert A. Simon (19162001)

    Herbert Simon earned a B.S. from the University of

    Chicago in 1936 and Ph.D. from the University of

    California at Berkeley in 1942. He then taught at the

    Illinois Institute of Technology and participated in the

    seminars of the Cowles Commission for Research in

    Economics at the University of Chicago along with

    Jacob Marschak and several future Nobel Laureates:

    Kenenth Arrow, Miton Friedman, Tjalling Koopmans,and Franco Modigliani. His serious participation in

    economic analysis came when he participated with

    Marschak in a study of the prospective economic effects

    of atomic energy. He moved to the Carnegie Institute of

    Technology in 1949 and worked there for the rest of his

    career.

    Simon was a quintessential renaissance man who

    made major contributions to a number of fields: applied

    mathematics, business and public administration,

    economics, information sciences, operations research,

    philosophy, political science, and psychology. Hecoined the terms satisficing and bounded rationality

    to explain human behavior and decision-making

    processes. He worked with Alan Newell to lay the

    foundations of artificial intelligence. In his book,

    Sciences of the Artificial, he used the natural science

    analog to create a scientific framework for designing

    and analyzing social systems. In 1978, Simon was

    awarded the Nobel Prize for his pioneering research

    into the decision-making process within economic

    organizations.

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