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The '''program ''' '''evaluation and review technique''' ('''PERT''') is a statistical tool used in [[project management]], which was designed to analyze and represent the [[task (project management)|tasks]] involved in completing a given [[project]].
OriginallyPERT was originally developed by Charles E. Clark for the [[United States Navy]] in 1958,; it is commonly used in conjunction with the [[Critical Path Method]] (CPM), thatwhich was also introduced in 1958.<ref name="origins">{{cite journal |last1=Kelley |first1=James E. |last2=Walker |first2=Morgan R. |last3=Sayer |first3=John S. |title=The Origins of CPM: a personal history |journal=Project Management |date=February 1989 |volume=3 |issue=2 |page=18 |url=https://www.pmi.org/learning/library/origins-cpm-personal-history-3762 |access-date=20 March 2024 |publisher=Project Management Institute }}</ref>
== Overview ==
PERT is a method of analyzing the tasks involved in completing a project, especially the time needed to complete each task, and to identify the minimum time needed to complete the total project. It incorporates uncertainty by making it possible to schedule a project while not knowing precisely the details and [[Duration (project management)|durations]] of all the activities. It is more event-oriented than start- and completion-oriented, and is used more for projects where time is the major constraint rather than cost. It is applied to very large-scale, one-time, complex, non-routine infrastructure projects, as well as [[R&D]] projects.
PERT offers a management tool,{{sfn|Kerzner|2009}}{{rp|497}} which relies "on arrow and node diagrams of ''activities'' and ''events'': arrows represent the ''activities'' or work necessary to reach the ''events'' or nodes that indicate each completed phase of the total project."<ref name="MB 1968" />
PERT and CPM are complementary tools, because "CPM employs one time estimation and one cost estimation for each activity; PERT may utilize three time estimates (optimistic, expected, and pessimistic) and no costs for each activity. Although these are distinct differences, the term PERT is applied increasingly to all critical path scheduling."<ref name="MB 1968" />
==History==
PERT was developed primarily to simplify the planning and scheduling of large and complex projects. It was developed forby the [[United States Navy Special Projects Office|U.S.]], Navy[[Lockheed SpecialAircraft]], Projectsand Office[[Booz Allen Hamilton]] to support the U.S. Navy's [[Polaris nuclear submarinemissile]] project.<ref name="MRCW 1959">Malcolm, D.Donald G.; Roseboom, J.John H.; RoseboomClark, C.Charles E. Clark,; [[Willard Fazar|W.Fazar, FazarWillard]].; "Application of a Technique for Research and Development Program Evaluation,", ''Operations Research'', Volvol. 7, Nono. 5, September–October 1959, pp. 646–669</ref><ref name="byte198205">{{Cite magazine |last1=Zimmerman |first1=Steve |last2=Conrad |first2=Leo M. |date=May 1982 |title=Programming PERT in BASIC |url=https://archive.org/details/eu_BYTE-1982-05_OCR/page/n466/mode/1up?view=theater |access-date=2024-12-29 |magazine=BYTE |pages=465–478}}</ref> It found applications throughout industry. An early example is the [[1968 Winter Olympics]] in [[Grenoble]] which used PERT from 1965 until the opening of the 1968 Games.<ref>[http://www.la84foundation.org/6oic/OfficialReports/1968/or1968.pdf 1968 Winter Olympics official report], p. 49. Accessed 1 November 2010. {{in lang|en|fr}}</ref> This project model was the first of its kind, a revival for the [[scientific management]], founded byof Frederick Taylor and later refined by Henry Ford ([[Fordism]]). [[DuPont]]'s CPM was invented at roughly the same time as PERT.
[[File:PERT Summary Report Phase 2, 1958.jpg|thumb|upright|''PERT Summary Report Phase 2'', 1958]]
Initially PERT stood for ''Program Evaluation Research Task,'' but by 1959 was renamed.<ref name="MRCW 1959" /> It had been made public in 1958 in two publications of the U.S. Department of the Navy, entitled ''Program Evaluation Research Task, Summary Report, Phase 1.''<ref>U.S. Dept.Department of the Navy., ''[https://web.archive.org/web/20151112203807/http://www.dtic.mil/dtic/tr/fulltext/u2/735902.pdf ''Program Evaluation Research Task, Summary Report, Phase 1].'' Washington, D.C.], Government Printing Office, Washington (DC), 1958.</ref> and ''Phase 2.''<ref>U.S. Dept.Department of the Navy., ''[https://catalog.hathitrust.org/Record/100954569 ''Program Evaluation Research Task, Summary Report, Phase 2].'' Washington, D.C.], Government Printing Office, Washington (DC), 1958.</ref> both primarily written by Charles F. Clark.<ref name="origins" /> In a 1959 article in ''[[The American Statistician]]'', [[Willard Fazar]], Head of the Program Evaluation Branch, Special Projects Office, U.S. Navy, gave a detailed description of the main concepts of PERT. He explained:
{{Blockquote|Through an electronic computer, the PERT technique processes data representing the major, finite accomplishments (events) essential to achieve end-objectives; the inter-dependence of those events; and [[Estimation (project management)|estimates]] of time and range of time necessary to complete each activity between two successive events. Such time expectations include estimates of "most likely time", "optimistic time", and "pessimistic time" for each activity. The technique is a management control tool that sizes up the outlook for meeting objectives on time; highlights danger signals requiring management decisions; reveals and defines both methodicalness and slack in the flow plan or the network of sequential activities that must be performed to meet objectives; compares current expectations with [[Schedule (project management)|scheduled]] completion dates and computes the probability for meeting scheduled dates; and simulates the effects of options for decision— before decision.<brref name="SDFJWM 1959">[[Willard Fazar]] cited in: Stauber, B. Ralph; Douty, Harry M.; Fazar, Willard; Jordan, Richard H.; Weinfeld, William; and Manvel, Allen D.; [https://www.jstor.org/stable/2682310 "Federal Statistical Activities"], ''The American Statistician'', 13(2): 9–12 (April 1959), pp. 9–12</ref>}}
[[File:PERT Guide for management use, June 1963.jpg|thumb|upright|''PERT Guide for managementManagement useUse'', June 1963]] ▼The concept of PERT was developed by an operations research team staffed with representatives from the Operations Research Department of [[Booz Allen Hamilton]]; the Evaluation Office of the [[Lockheed Martin Space Systems|Lockheed Missile Systems Division]]; and the Program Evaluation Branch, Special Projects Office, of the Department of the Navy.<ref name="SDFJWM 1959">[[Willard Fazar]] cited in: B. Ralph Stauber, H. M. Douty, Willard Fazar, Richard H. Jordan, William Weinfeld and Allen D. Manvel. "[https://www.jstor.org/stable/2682310 Federal Statistical Activities]." ''The American Statistician'' 13(2): 9–12 (Apr., 1959), pp. 9–12</ref>}}
Ten years after the introduction of PERT, the American [[librarian]] Maribeth Brennan publishedcompiled a selected [[bibliography]] with about 150 publications on PERT and CPM, which had beenall published between 1958 and 1968. <ref Thename="MB origin1968">Brennan, Maribeth; ''PERT and developmentCPM: wasa summarizedselected asbibliography'', follows:Council of Planning Librarians, Monticello (IL), 1968, p. 1</ref>▼
For the subdivision of work units in PERT<ref> Cook, Desmond L. Cook (1966),; ''Program Evaluation and Review Technique .'' , 1966, p. 12</ref> another tool was developed: the [[Work Breakdown Structure]]. The Work Breakdown Structure provides "a framework for complete networking, the Work Breakdown Structure was formally introduced as the first item of analysis in carrying out basic PERT/ COSTCPM."<ref>[[Harold Bright Maynard |Maynard, Harold Bright]] (1967), ''Handbook of Business Administration .,'' 1967, p. 17</ref> ▼▲[[File:PERT Guide for management use, June 1963.jpg|thumb|upright|''PERT Guide for management use'', June 1963]]
▲Ten years after the introduction of PERT, the American [[librarian]] Maribeth Brennan published a selected [[bibliography]] with about 150 publications on PERT and CPM, which had been published between 1958 and 1968. The origin and development was summarized as follows:
{{Blockquote|PERT originated in 1958 with the ... [[UGM-27 Polaris|Polaris missile]] design and construction scheduling. Since that time, it has been used extensively not only by the [[aerospace industry]] but also in many situations where management desires to achieve an objective or complete a task within a scheduled time and cost expenditure; it came into popularity when the algorithm for calculating a maximum value path was conceived. PERT and CPM may be calculated manually or with a computer, but usually they require major computer support for detailed projects. A number of colleges and universities now offer instructional courses in both.<ref name="MB 1968">Brennan, Maribeth, ''PERT and CPM: a selected bibliography,'' Monticello, Ill., Council of Planning Librarians, 1968. p. 1.</ref>}}
▲For the subdivision of work units in PERT<ref>Desmond L. Cook (1966), ''Program Evaluation and Review Technique.'' p. 12</ref> another tool was developed: the [[Work Breakdown Structure]]. The Work Breakdown Structure provides "a framework for complete networking, the Work Breakdown Structure was formally introduced as the first item of analysis in carrying out basic PERT/COST."<ref>[[Harold Bright Maynard]] (1967), ''Handbook of Business Administration.'' p. 17</ref>
==Terminology==
During project execution a real-life project will never execute exactly as it was planned due to uncertainty. This can be due to ambiguity resulting from subjective estimates that are prone to human errors or can be the result of variability arising from unexpected events or risks. The main reason that PERT may provide inaccurate information about the project completion time is due to this schedule uncertainty. This inaccuracy may be large enough to render such estimates as not helpful.
One possible method to maximize solution robustness is to include safety in the baseline schedule in order to absorb the anticipated disruptions. This is called ''proactive scheduling''., Purely proactive scheduling is unrealistic; incorporating safety in a baseline schedule whichhowever, allowsallowing for every possible disruption would leadbe tovery aslow baselineand schedulecouldn't withbe aaccommodated veryby largethe make-spanbaseline schedule. A second approach, termed ''reactive scheduling'', consists of definingdefines a procedure to react to disruptions that cannot be absorbed by the baseline schedule.
== See also ==
[[Category:Booz Allen Hamilton]]
[[Category:Operations research]]
[[Category:Management cybernetics]]
[[Category:Engineering management]]
[[Category:Management science]]
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