Università di Padova SECOND CYCLE DEGREE PROGRAMME (MSC LEVEL) IN ENVIRONMENTAL ENGINEERING ENVIRONMENTAL IMPACT ASSESSMENT Multicriteria Analysis (MCA) A.A. 2014-2015 Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Introduction MULTI CRITERIA METHODS FROM SINGLE TO MANY GOALS Classical methods of analysis (to solve managerial decision problems) generally based on linear singlecriterion optimization Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Introduction Example evaluation of two different processes for electricity production, having as limits emissions of pollutants and the availability of fuel is expressed with: • A function to maximize: Max f(x), where x is the energetic efficiency; • Constraints: - QC<dC, where QC is the quantity of coal used and dC its availability; - QM<dM where QM is the quantity of methane used and e dM its availability; - Emissions < table values required by law. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Introduction IN A COMPLEX EVALUATION: • linear optimization may be too rigid function • not always possible to identify a single objective • or is not quantifiable, • constraints are not always explicit, • in general the reality is not perfectly modeled. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Introduction Possible solutions: • use of non-linear programming models (complex and always based on a perfect quantification of objectives), • Use of (optimization) models with several objectives. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models MULTI CRITERIA MODELS "If something is considered valid at all, it definitely is for several reasons" (Howard Raiffa). Are based on the idea that in a complex decision problem (EIA, SEA, etc.) there may be many aspects, not all traceable to a single goal. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models ADVANTAGES: • Takes into account different priorities and preferences (participation) • Highlights the different components of the problem and their relationships, organizing and synthesizing these data in an organic way (rationality) • Makes explicit all the data processed (transparency) • It reduces the arbitrariness of decisions (reproducibility) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models DISADVANTAGES: • Might “exagerate” any juxtapositions, • lends itself to manipulation (like all models) • simplifies reality (like all models) • Some techniques are very complex, • Sometimes the process is even "too" transparent (!). Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models WHY IMPORTANT IN THE EIA ? • allow to synthesize a lot of information • take into account several objectives • uses arrays of assessment (useful way to organize and communicate information ) • decision closer to reality (compared for example to the cost/benefit analysis) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models HOW DO THEY WORK ? 1. 2. 3. the object of analysis is broken down into simple factors, criteria, which describe it exhaustively These criteria are then analyzed separately Several alternatives are then evaluated with respect to each single criterion (of choice) SCOPE OF THE ANALYSIS CRITERION C3 CRITERION C2 CRITERION C1 OPTION C OPTION B OPTION A Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models HOW DO THEY WORK ? Analyze OPTION A with respect to: • Criterion C1 • Criterion C2 • Criterion C3 Analyze OPTION B than .... Etc. SCOPE OF THE ANALYSIS CRITERION C3 CRITERION C2 CRITERION C1 OPTION C OPTION B OPTION A Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Appendice: Multi Criteria Models The criteria are the means by which the various alternatives are compared to each other over the objective of the decision maker Definition: a criterion is a real function f such that it is meaningful to compare two alternatives a and b of a set of alternatives A with respect to a particular point of view, solely on the basis of the values of f(a) and f(b) In practice, the criteria represent the environmental components, the costs, the social aspects, etc.. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Multi Criteria Models CONVENTION: criteria and attributes are synonyms Theory of Operational Research: - multi-criteria analysis ! problem of choice among a finite number of alternatives - multi-objectives analysis ! decision problem inherent infinite alternatives in practice are also synonyms ! Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE PROCEDURE IN DETAIL Five main phases: 1. Definition of evaluation matrix 2. Standardization of data 3. Assigning weights 4. Calculation of sorting 5. Sensitivity analysis Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE EVALUATION MATRIX (impact matrix, analysis matrix, evaluation matrix, score matrix, appraisal table) nxm two-dimensional array, which crosses the n objectives (or criteria) with the m option of choice. presenting nxm indicators with different units of measurement (quantitative, qualitative or mixed) Crit. A Crit. B Crit. C Alt. 1 0.4 60 ++ Alt. 2 0.8 40 - Alt. 3 0.6 65 + Università di Padova LASA - DII For example: C1: land in hectares C2: Cost in millions of euros C3: impact on the landscape Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail EVALUATION MATRIX Not only serve to identify the impacts, but also to organize the data possibly in a very complex way. Evaluation matrices consist of two-dimensional checklists: a list of "activities" (project, plan or program) is related with a list of components (environmental, social, economic). Two-dimensional representation of cause-effect relationships between planning/programming activities and the social and environmental factors potentially subject to change. For each intersection between the elements of the two lists is possible to verify the actual presence of the impact (reporting matrix) and possibly already give an assessment (evaluation matrix, impacts matrix, etc.). Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail EVALUATION MATRICES • Several methods for their construction • Methods generally based on a hierarchical system: from generic elements (environmental components, phases of plan, etc..) descend in detail (breakdown, "forward") • Sometimes is also used the reverse process ( "backward"). • is often based on scientific literature and case studies Typically a matrix of impacts may be disaggregated by: • Temporal Horizons (stages) • Geographical areas • Typologies • Actors Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail STANDARDIZATION • needed to make data in the array homogeneous and operational. • the data are transformed into dimensionless values (convention) with one or more logical-mathematical function. Two main types: 1. Linear standardization 2. Value function (utility) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail 1. Linear standardization Simple mathematical functions that operate on values in each column of the matrix. Can vary from column to column of the matrix Standardizzazione Funzione Row maximum x x max Ideal value ( x − xmin .id . ) ( xmax .id . − xmin .id . ) Average value x x mean interval standardisation ( x − x min .row ) ( x max .row − x min .row ) Additive constrain x ∑ xrow Vector normalisation x x2 Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail 2. Value/utility function • Assign to each indicator value a corresponding score of merit/preference/utility dimensionless, between 0 and 1. • Necessity to define a function for each indicator (e.g., function “dose-response”). • It is said "value" when the data are deterministic, "utility" when stochastic • The utility measures the satisfaction of the decision maker 1 a 1 b 1 0.8 Quality 0.6 0.4 0.2 0 0 0 Min. Max . Min. Max . 0 0.05 0.10 0.15 0.20 0.25 Average annual concentration Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail 2. Value/utility function • • • Certain functions are derived in an objective way by laboratory tests (e.g. the "dose response"); others are necessarily subjective (aesthetic value, social tolerance, etc..) and therefore subject to change depending on the evaluator. Although subject to some ambiguity, these latter are widely used in evaluations of sustainability. The main difference between the two types of normalization is that in the first case, the functions may (but need not) vary from column to column of the matrix in the second case, you define a function for each indicator. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS • • • • are dimensionless numerical values; measure the priorities of the various aspects of the problem (the criteria); never have absolute but only relative value; are the marginal rate of substitution between the various criteria. Example: C1=30 C2=10 therefore C1= 3 C2 or C1/C2=3 Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Three main classes of techniques for assignment: 1. 2. 3. Università di Padova LASA - DII Direct assignment, Comparison in pairs, Methods based only on a ranking (even if incomplete). Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Direct assignment is the easiest method (but more "ambiguous") weights are assigned directly based on a predetermined scale of scoring (1 to 100, 1000, etc.) or redistributing this score among all the criteria (sum equal to 100, 1000, etc...) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Comparison in pairs: • The criteria are compared in pairs and a relative score is assigned. • This builds a matrix of paired comparisons square and symmetrical about the main diagonal. • The values of each row of the array are then aggregated into a final vector using functions like: maximal eigenvector, least squares, etc.. Crit. A Crit. B Crit. C Crit. A 1 1/2 7 0.6 Crit. B 2 1 3 0.2 Crit. C 1/7 1/3 1 0.2 Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS By convention: - array elements are positive; - Aij=1/Aji; - The diagonal values are equal to unity.. Consequently, the number of comparisons required is: Università di Padova LASA - DII Crit. A Crit. B Crit. C Crit. A 1 1/2 7 Crit. B 2 1 3 Crit. C 1/7 1/3 1 Environmental Impact Assessment Environmental Engineering [(n·(n-1)/2] a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Methods based only on a ranking (even if incomplete). - - - Less common and very complex No quantitative assessment only order of importance It is assumed that the sum of the weights is equal to 1 - Three main approaches: Università di Padova LASA - DII 1. Expected value 2. Extremal value 3. Random weights Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Expected value: Given the premise, it assumes a distribution of values equally likely Average values are those that approximate satisfactorily the vector of weights sought. NB The weights do not depend on the nature of the criteria or the preference of the decision maker, but only by their number and order. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Extremal values: Only the extreme weights are considered; Calculate the resulting orders. NB All weights, and related rankings, included between these extremes, comply with the order of priorities imposed. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Random weights: It is generated a large number of random rankings, and all the possible combinations of weights satisfying the initial assumptions are calculated For each of these sets of weights it is calculated the resulting ranking of alternatives and the probability for each ordering. NB The ordering is derived from a comparison of probabilities Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail RANKING CALCULATION The basic mechanism: • Combine weights and standardized indicators for any alternative; • Compare alternatives to each other based on values obtained. Two main techniques: 1. the weighted sum 2. Indices of “concordance” and “discordance” Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Weighted sum: • • • "prescriptive" technique (based on transitivity, completeness), extremely common and simple Sometimes it is "too" simple and can be unfaithful to the complex reality Each indicator is multiplied by the respective weight and summed with those of the same line Aj=Σiwiaij Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” • “descriptive” techniques (depending on the assumption of incomparability and intransitivity) • Comparison in pairs of all the alternatives by evaluating two different indices: a. Index of concordance b. Index of discordance Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” The concordance (Con) measures the satisfaction of choosing A1 than A2 (with respect to the criteria c1, c2, etc.). Is equal to the sum of the corresponding weights Coni,j=Σnwn The discordance (Dis) measures the regret in dismissing A2 compared to A1 and is (usually) measured as the maximum difference between the values of the indicator of those criteria for which is expressed the regret of choosing the second option than the first (usually but not necessarily, normalized to the maximum difference of column) Disi,j= max|ci-cj| Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” Construction of two matrices of pairwise comparisons (that of discordance and that of concordance and aggregate these values respectively into two vectors, whose elements are the indices of concordance (Ic) and the indices of discordance (Id), obtained according to the formulas: Icj=ΣiConj,i - ΣiConi,j Idj=ΣiDisj,i – ΣiDisi,j Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” The alternatives are then sorted into two lists: 1. increasing index of concordance 2. decreasing index of discordance. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS EXAMPLE: Indices of “concordance” and “discordance” three alternatives [A1, A2, A3] and three criteria [C1, C2, C3] whose weights are respectively [0.2, 0.3, 0.5] (direct assignment). M = Con i,k = mi,k = ∑ w j j C1 A1 80 A= A2 40 A3 60 C2 0.6 € 0.8 0.1 Impact matrix Università di Padova LASA - DII C3 A1 A2 A3 10 A1 − 0,2 0,5 M = € 40 A2 0,8 − 0,8 35 A3 0,5 0,2 − Concordance matrix (M) N = Disi,k = n i,k = max akj − aij A1 A1 − N= A2 1 A3 0,7 A2 A3 1 0,8 − 0,5 1 − Discordance matrix (N) Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 C1 0,2 80 40 60 weights A1 A2 A3 C2 0,3 0,6 0,8 0,1 180 normalized by1column sum normalized by1column maximum 0,4 0,2 0,3 1 0,5 0,75 Università di Padova LASA - DII C3 0,5 10 40 35 1,5 0,4 0,5 0,1 0,75 1 0,125 A1 A2 A3 85 Weighted(sum 0,1 0,3 0,5 0,4 0,4 0,3 0,25 1 0,875 0,6 0,9 0,6 A1 A2 A3 A1 A2 A3 % 0,8 0,5 1,3 0,2 % 0,2 0,4 0,5 0,7 0,8 1,6 % 0,7 1,3 Concordance A1 !0,6 A2 1,2 A3 !0,6 % 1 0,7 1,7 1 % 1 2 0,8 1,8 0,5 1,5 % 1,7 1,3 Discordance 0,1 $0,5 0,4 0,7 C2 0,29 8 8 8 0,71 0,13 30 C3 1,00 0,83 8 8 8 Maximum'difference cfr A1''A2 A1''A3 A2''A1 A2''A3 A3''A1 A3''A2 Environmental Impact Assessment Environmental Engineering 40 C1 8 8 1 0,5 0,5 1 MAX 1,0 0,8 1,0 0,5 0,7 1,0 a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS EXAMPLE: Indices of “concordance” and “discordance” three alternatives [A1, A2, A3] and three criteria [C1, C2, C3] whose weights are respectively [0.2, 0.3, 0.5] (direct assignment). For the discordance It is normalized the difference of the values of the indicator with the maximum difference of the criteria indicator (for those criteria that “lose”) and then it is choosen the maximum Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” EXAMPLE Coni ,k = mi ,k = ∑ w j j M = A1 A1 A2 A3 − 0,2 0,5 A2 0,8 − 0,8 A3 0,5 0,2 − Concordance matrix (M) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” EXAMPLE Disi ,k = ni ,k = max a kj − aij A1 A1 − N= A2 1 A3 0,7 A2 A3 1 0,8 − 0,5 1 − Discordance matrix (N) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS Indices of “concordance” and “discordance” EXAMPLE Ic(i ) = ∑ mi , j − ∑ m j ,i Id (i ) = ∑ ni , j − ∑ n j ,i j Università di Padova LASA - DII j j A1 − 0,6 A2 1,2 A3 − 0,6 A1 0,1 A2 − 0,5 A3 0,4 Concordance Discordance vector vector Environmental Impact Assessment Environmental Engineering j a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS EXAMPLE (the same): weighted sum (0,2) (0,3) (0,5) C1 A1 80 A= A2 40 A3 60 C2 0.6 0.8 0.1 C3 10 40 35 (0,2) (0,3) (0,5) C1 C2 C3 0.4 0.4 0.1 (0,4X0,2)+(0,4X0,3)+(0,1X0,5)=0,3 0.2 0.5 0.5 (0,2X0,2)+(0,5X0,3)+(0,5X0,5)=0,4 0.3 0.1 0.4 (0,3X0,2)+(0,1X0,3)+(0,4X0,5)=0,3 A3 Results standardized only on the criteria (column or row sum) A2 A1 0 Università di Padova LASA - DII 0,2 Environmental Impact Assessment Environmental Engineering 0,4 0,6 0,8 1 a.a. 2014/2015 The procedure in detail THE ASSIGNMENT OF WEIGHTS ESEMPIO (the same): weighted sum (0,2) (0,3) (0,5) 1 0,75 0,25 (1X0,2)+(0,75X0,3)+(0,25X0,5)=0,6 (0,55) 0,5 1 1 (0,5X0,2)+(1X0,3)+(1X0,5)=0,9 0,75 0,13 0,88 (0,75X0,2)+(0,13X0,3)+(0,88X0,5)=0,6 (0,63) Results standardized by column maximum Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail SENSITIVITY ANALISYS is particularly indicated in cases of uncertainty and ensure a proper evaluation of all possible points of view of the problem. Operated on the results to see what changes in the model of analysis can generate substantial differences in performance of the alternatives. "Point of inversion": for what values of criteria and indicators, there is a reversal of the order of alternatives in the rankings. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 SENSITIVITY ANALISYS Purpose: identify the most sensitive components of the model e.g. parameters, weights, criteria ⇓ that make rankings vary Sensitivity: (condition number): S x = Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering ∂x ∂P x P a.a. 2014/2015 The procedure in detail SENSITIVITY ANALISYS Three main types of sensitivity analysis: 1) on the method: apply a different method of data standardization and (when possible) of computation of final scores. Is used to control the dependence of the results from the method of calculation. 2) on the criteria: add or delete some decision criteria. Is used to check if basic criteria are missing 3) on the weights (most used): change the ratings on certain criteria. Allows to notice the degree of influence of each factor on the final decision. Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 The procedure in detail SENSITIVITY ANALISYS Sx measures the sensitivisty of alternative x to criteria P ! Investigate at least 2 levels of variation, e.g. ± 30%, ± 60% ! Determine more accurately the values of the more sensitive criteria ! Further levels of variation for more sensitive criteria Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 DO 2 CBOD NH3 CN NO3 ON 1 PARAMETRI Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering CARICHI E_ON E_NO3 E_NH3 E_DO E_CBOD Fl_ON Fl_NH3 Fl_CBOD td kd t71 k71 k2 t1R K1R t1C k1C t12 k12 tS SOD 0 CONDIZIONI AL CONTORNO a.a. 2014/2015 Practical aspects IN PRACTICE SOME MODELS PRESCRIPTIVE SMART (Simple Multi Attribute Rating Technique) – SMARTS – SMARTER AHP (Analytic Hierarchy Process) – ANP (Analytic Network Process) etc. (based on weighted sum, value function, utility functions, direct assignment, pairwise comparisons) (IDEAL VALUE METHOD) DESCRIPTIVE ELECTRE (I, II, III IV V) Regime EvaMIX etc. (based on concordance and discordance indices, random assignment, expected value, etc.) Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Practical aspects IN PRACTICE PRODUCTS SOFTWARE Infoharvest (SMART) EC Pro (Expertchoice) (AHP) Macbeth Etc. DSS Definite Vispa GIS Etc Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015 Conclusions References • Bana e Costa C. A. (ed.) (1990), Reading in Multiple Criteria Decision Aid, Spring-Verlag, Germany. • Luria P ., Morara M. (2002), Analisi A Multi Criteri. Documento Informativo, Padova: documento interno ARPA. • Voogd H. (1983), Multicriteria Evaluation for Urban and Regional Planning. London, UK: Pion Limited, Università di Padova LASA - DII Environmental Impact Assessment Environmental Engineering a.a. 2014/2015
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