Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFTED,AC/243(Panel-8)TR/7- 42 -Volume 13.2.10 Relationship to system performance requirements73. The results of human engineering efforts must be related to system performance.Erickson (1986) argues that system component and operator performance are not explicit in theupper levels of any systems analysis. He describes an approach to developing a "capabilityhierarchy" starting with a functional analysis, and decomposing the performance requirementsfrom that level. He notes that it is necessary to go down at least two levels in the hierarchy beforeoperator performance criteria become apparent (see Fig. 3.4). Therefore, there may be no directarelationship between system performance criteria and operator task performance unless theconnection is made explicit by analysis. 3Specify measures--1- ofeffectivenessDefine mission* functional description* system requirements escrioe systemblock diagram-4 * functional analysis* operating profile* maintenance orofileadea SAcquire data l I dentify important factors*weather data L -* operational rSfactors*data from simila sytm*mitnnce f actors -11human performc daa*-environmental factors*sea state. terrain. etc..- trainino factor-,sConstruct model|Exercise model- assumptions/definitions * parameter variation. msysiotemstates . operator performanceytmsae- estimate effeactiveness. sub-modelsFigure 3.4: Principal activities required to evaluate systems effectivenessa(after Erickson, 1986)t74. Table 3.1 shows the links between the individual human engineering analyses andbsystem performance criteria identified for the techniques reviewed in Volume 2. 'Me informationaappears to support Erickson's analysis. In most cases the link from human engineering anaiysesto system performance requirements is not direct. 'Me analyses differ in the scale ofmeasurement used (Siegel, 1956). Functional analysis techniques are restricted to either nominalscales, i.e., the identification of classes or categories of function, or ordinal scales, i.e.,qualitative measures of performance. Distances and clock times in a mission profile, or thenumber of tokens in a Petri net, are interval scale measures because they are not related to a zeronpoint by ratios. Techniques such as SAINT provide ratio scale data such as task completionatimes and probabilities. Many of these measures require an analysis of system performancearequirements to identify the influence of operator performance on the system.rti