1. Introduction
Managing a contemporary town with a view to achieving its sustainable development requires that the urban authorities should have to account for a number of interdependencies between factors influencing or affecting the outcome of decisions being made [
1]. Thus, they have to account for economic, social, and environmental factors [
2]. Hence, in their decision making they will have to be knowledgeable in urban planning, spatial development, technology, ecology, sociology, and social psychology, among others. Such knowledge is also needed when new tools, such as a participatory budget, are about to be implemented.
A participatory budget, often also called a “citizen budget” (CB), is a decision-making process involving citizens in the life of their town. In such a CB scheme, citizens co-create their town’s budget, by making joint decisions concerning allocation of a certain portion of the public budget [
3]. A portion of public funds set out by the town authorities is allocated to implement those projects that take into consideration the needs that residents of a given quarter, street, or estate have. The implementation of such projects entails a risk, as it neglects the outcome of selected CB projects to be completed for the town’s sustainable development. Therefore, in order for the CB projects to account for sustainability, citizens should be informed which of the submitted projects are best in regard to the sustainable development of their town, quarter, or estate. A decision-making problem arises, which in order to be solved, needs comprehensive knowledge from a number of areas. It is advisable that the emerging decision-making issue be presented to experts who will evaluate the CB projects submitted. To that end, the experts should use available tools, for instance the known methodology MCDA (multi-criteria decision analysis), AHP (Analytic Hierarchy Process) [
4,
5], PROMETHEE (Preference Ranking Organization METHod for Enrichment of Evaluation) [
6], TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) [
7], or their variants operating on fuzzy numbers [
8] employed successfully to solve similar decision-making problems [
9,
10,
11]. Such fuzzy approaches to decision making are particularly important in decision-making problems where uncertainty arises [
12,
13,
14].
The methodological contribution of this paper is to propose and verify a new MCDA method, called PVM-VSI (Preference Vector Method computed in Vector Space of Increments), based on vector calculations. This method, by studying deviations of variant evaluations, allows one to perceive the decision maker’s uncertainty in the decision making process and account for it in the final evaluative outcome. In practical terms, we verify the proposed method in a decision-making problem to select and evaluate citizen budget projects in a specific city in Poland. The selection was based on a sustainability assessment of the individual variants with the use of PVM-VSI. The obtained results were compared with the results of three other methods, i.e., Fuzzy AHP [
15], Fuzzy TOPSIS [
16,
17], and NEAT F-PROMETHEE (New Easy Approach To Fuzzy PROMETHEE) [
18,
19].
The rest of the paper is organized as follows.
Section 2 presents examples of applications of the MCDA method in assisting solutions to decision-making problems related to urban development.
Section 3 describes the PVM-VSI method, applied to assign ranks to projects submitted within the framework of a participatory budget. In
Section 4, a decision-making problem related to drawing up a rank of CB projects is described.
Section 5 shows research results produced by the PVM-VSI method.
Section 6 is devoted to research in which the Fuzzy AHP, Fuzzy TOPSIS, and NEAT F-PROMETHEE methods are used, with a view to comparing outcomes obtained by means of the methods with the PVM-VSI method applied. In addition,
Section 6 presents global sensitivity and uncertainty analyses of the solution obtained using the PVM-VSI method. The paper is rounded off with conclusions from the research.
2. Literature
Multi-criteria methods are widely used in solving decision-making problems related to sustainable urban development. The reference literature has examples of the MCDA method used in solving decision-making problems involving participation of funds [
10], or similar ones related to a choice of urban developmental priorities, such as allocation of urban land use [
20], as well as the extent of land use zones in an urban planning scenario [
21].
Another group of decision-making problems where MCDA methods are applied are public area development. The literature often quotes examples of MCDA methods used in issues concerning the selection of a new hospital site [
15], hospitals or joint-venture medical institutions [
22], places for new emergency services to be erected [
23], places to house a new firefighting station [
24], or the selection of the very project for construction of that type [
9].
MCDA methods were also used in assisting urban development not related directly to emergency services, but of importance to the standard of living of residents in a given region where that project is to be implemented. These construction investments were related to environmental protection and commerce: selection of a landfill place [
25], selection of a healthcare waste disposal facility [
26], a wastewater treatment plant [
27], a wind farm [
28], and a shopping center [
29]. A considerable group is made up of construction projects related to transport facilities, where MCDA methods were used to assist decision makers in their decisions, such as selection of a strategy (concept) of urban logistics [
11,
30,
31,
32], an urban distribution center [
33,
34], or a public parking place [
35].
MCDA methods most frequently used in decisions concerning urban sustainable development are: AHP used in previous studies [
11,
21,
24,
25,
28,
32,
35], its fuzzy version (Fuzzy AHP) [
9,
15,
21,
22,
23,
26,
29], and a fuzzy version of the TOPSIS method used in other previous studies [
10,
11,
20,
23,
26,
27,
29,
31,
33,
34]. Other examples of the use of decisions made in this manner by means of the ELECTRE method [
24], PROMETHEE [
28], ANP (Analytic Network Process), Fuzzy DEMATEL (DEcision MAking Trial and Evaluation Laboratory), Fuzzy VIKOR (Vlse Kriterijumska Optimizacija kompromisno Resenje which means multi-criteria optimization and compromise solution, in Serbian) [
30], and THOWA (2-Tuple Hybrid Ordered Weighted Averaging) [
34].
Often hybrid solutions are used along with MCDA methods in which the GIS (Geographical Information System) is used [
15,
20,
25,
35], or two methods are combined with a view to finding an optimal solution [
11,
23,
24,
28,
29,
30].
Table 1 depicts the basic characteristics of the MCDA applications in the problems related to urban development.
3. Methodological Framework
The PVM-VSI method was used as a methodological framework to evaluate and rank projects submitted for participatory budgeting. The presented method is a modification and extension of the original PVM [
36,
37]. It is a multi-criteria method assisting a decision maker in making a decision by providing to him a rank of decision variants. The implemented modification allows the decision maker to account for uncertainty in evaluation of decision criteria. The individual steps of the PVM-VSI method are shown in
Figure 1.
On the basis of the questionnaire addressed to respondents, comparative matrices are produced, where l is the number of criterion being compared. Entries of these matrices are , where i and j are numbers of decision variants. Information contained in those matrices is often inconsistent, which is derived from inconsistent responses. This inconsistency should be reflected in the calculation result. To that end, on the basis of the matrix , matrix is constituted. The matrix is an intermediate matrix of the comparison in reference to the variant .
In the rows of the matrix there are comparisons of the ith variant, with reference to the variant . In the columns there are successive kth decision variants.
The matrix
is obtained from the following formula (1):
where
is an entry of the matrix
.
Matrices
are normalised in order to reduce their values to compatibility, in effect to arrive at the matrix
(2):
where
is an entry in the matrix
, while
o is the number of the decision variant to which all matrices
are reduced.
On the basis of the matrix
, vectors of average evaluations
are calculated for individual decision variants (3).
where
is a vector representing the
jth decision variant, whereas
is an element of that vector, while
N is the number of decision variants.
A matrix containing covariants
is also produced for individual variants, regarding the individual criteria (4):
where
is an entry of matrix
.
For the calculated vectors
a motivation preference vector for average value
is determined (5):
where
i denotes a specific criterion,
is the vector element
, and
means the third quartile calculated with respect to the variant
j.
Furthermore, a demotivation vector of preference for average values
is determined (6):
where
i denotes a specific criterion,
is the vector element
, and
means the first quartile calculated with respect to the variant
j.
The vector
is calculated as the difference between the vectors
i
(7):
On the basis of that vector, the vector
is determined by reducing it to a unit vector (8):
is the magnitude of the vector
(9):
where
i denotes a specific criterion,
is an element of vector
.
The vector
allows determination of the transformation matrix
T (10):
The matrix is always a square matrix.
Multiplying the coordinates of the vector
by the matrix
T yields the vector of evaluation of a given decision variant
(11):
All elements of the vector , apart from the first one , equal nil. The element is the evaluation of a given decision variant and is comparative in its function. It should be noted that the best solution has the lowest value, so the issue of minimization is considered. In practice, the best option is considered to be the one over which the other variants in pairwise comparison matrices outweigh the least (compare formulas (1)–(3)).
Likewise, the matrix
can be transformed, so that the output is the matrix
(12):
where
is an element of the matrix
.
Elements of
, for which
i =
k are variants. On that basis, the standard deviation of the evaluation of decision variants after transformation can be calculated (13):
All elements apart from the first one equal nil. The element is a standard deviation of the evaluation of a given decision variant.
Standard deviation is a measure of the variability of a given phenomenon, object, or objects. That variability can result from changes in the parameters of an object over time, measurement error, and if there are more objects, it may represent their heterogeneousness. If evaluation of objects proves to be difficult, it may stand for a degree of uncertainty of that evaluation. The method presented above, in which comparative matrices are constructed, is used to calculate a deviation standard to represent the degree of uncertainty of evaluation which the PVM method requires. The classical PVM method allows construction of a rank of decision variants. That rank, however, does not allow for a degree of uncertainty of evaluation to be accounted for. A modified method allows determination of a standard deviation for each decision variant included in the rank. Because in this method the standard deviation is at the same time a measure of uncertainty of the evaluation of decision variants, the very rank itself can be interpreted as a measure of uncertainty of its place within the rank. That uncertainty is a product of the decision maker’s uncertainty. Two decision variants that are close to one another in the rank, but characterized by a considerably large standard deviation, can thus be qualified as equivalent.
4. Decision Problem
The objective behind the research performed was to create a rank of projects submitted under a citizen budget and to make conclusive decisions as to which is best. Those projects that come up in hierarchy are more suited to influence urban sustainable development. Hence, they should be given priority by citizens and urban authorities in implementing a citizen budget. This research is meant to assist a decision maker in making their decision in a scenario where they must decide which project to select on the basis of a number of criteria. The criteria are but subjective evaluations by the decision maker in accordance with the scale adopted for the research. This may be related to how precise the evaluations by the decision maker are. Use of the PVM-VSI method is to make it easy for the decision maker to create a rank of projects and select those which will best suit the development of the town, and, indirectly, would be beneficial for the town’s people.
The decision maker evaluated by means of five criteria the same number of decision variants. The projects (variants) in the study were evaluated in accordance with the following criteria:
C1—spatial order: a criterion on the basis of which the projects were evaluated as to their impact on sorting out the urban space and on how well the constituents of the space are harmonized;
C2—modernization (revitalization): this criterion accounts for the impact that projects would exert on improving aesthetic assets of the town, estate, quarter, or street to which projects apply, by increasing their value in use and advantageous transformations in the area included in the project;
C3—environmental and nature protection: a criterion that is used to evaluate projects regarding their impact on nature and the environment, surrounding greenery, inland water, and fauna management in the area concerned;
C4—sport and tourism: a criterion used in evaluation of the impact of projects on the physical wellbeing of those who live in the area concerned, and to improve the attractiveness of the environs in the eye of tourists in the area;
C5—culture: a criterion which is used to evaluate the projects in the sense of what bearing they have on spiritual development of people to whom the project may concern.
The criteria here were selected for the research in such a manner that they could be used in the evaluation of the variants on their impact on the economic, social, and environmental milieus included.
Five decision variants were evaluated according to the criteria presented above:
A1: construction of a walking path along the river Warta from the East Boulevard to the Lubuski Bridge;
A2: a swimming pool within the river Warta water current;
A3: improvement in bicycle urban infrastructure;
A4: integrative playground for handicapped children;
A5: pro-eco revitalization of Słowiański Park.
These projects were the most interesting ones taken out of the pool of all projects submitted under the Citizen Budget 2018, Gorzów town. A number of projects were selected, which was dictated by the number of comparisons that would have to be drawn up; should all the submitted projects be included in the research, the duration of the very research would be extensively prolonged. The core of the research was not the selection of the most interesting projects, but a comparison of the proposed method assisting decisions with methods used so far in multi-criteria decision problems, where selection criteria are not quantified. Hence, the scope of projects could be narrowed down to a few of the most interesting projects out of the pool of all projects submitted under the 2018 CB.
5. Results
The research had nine stages. The first one was to define the weights of the individual criterion. In this case it was assumed that all criteria would have the same importance to the decision maker; thus, the criteria weights are equal. This can be interpreted as lack of weight.
Across stage two, the decision maker—taking advantage of a poll method—was asked to make pairwise comparisons of the decision variants as defined above. The variants were compared in accordance with the criteria specified above. This stage’s output produced five comparison matrices. The comparison matrix for the criterion
C1 (spatial order) is presented in
Table 2. The other pairwise comparison matrices are included in
Appendix A.
In the stage to follow, on the grounds of the pairwise comparison matrices, intermediate comparison matrices were constructed. The objective was to account for inconsistency of comparison matrices resulting from inconsistency in poll responses in the calculation results. An example of an intermediate comparison matrix is presented in
Table 3.
Stage four consisted of performing calculations on the basis of the matrices shown above, average evaluation vectors for the individual decision variants. The average evaluation vectors are presented in
Table 4.
In the stages to follow, on the basis of the average evaluation vectors, a covariance matrix can be created for individual variants within the framework of individual criterion, as well as motivation and demotivation preference vectors. An example of a covariance matrix for the variant
A1 is given in
Table 5.
Table 6 and
Table 7 show motivation and demotivation vectors, respectively.
The successive stage was to calculate the difference between the vectors as above; that is, the vector
. It is presented in
Table 8.
In the successive step, on the basis of the vector
and the value of the normalised motivation vector, the vector
was determined. The values of that vector are given in
Table 9.
With the vector
known, it is possible to determine a transformation matrix
T. That matrix is given in
Table 10.
On the basis of the matrix vectors, average evaluations for successive decision variants and a transformation matrix of the vector of the evaluation of a given decision variant were calculated. All elements of the evaluation vector, apart from the first one, equal nil. The first one is evaluation
of a given decision variant and is used to compare decision variants. The evaluations obtained by the individual decision variants are given in
Table 11 and
Figure 2. However, having a covariance matrix and a transformation matrix, variances can be calculated for successive decision variants, on the basis of which a standard deviation can be calculated for individual variants. Standard deviation is a value informing which area the value of evaluation calculated for a given decision variant can change in this study. Variance values (
var) obtained in this study and the standard deviation values (
σ) obtained from successive variants are gathered in
Table 11.
7. Conclusions
This paper presents a new method called PVM-VSI, used to assist multicriteria decisions. The procedure used in the PVM-VSI method has been described and used to create a rank of projects submitted within the framework of a Citizen Budget, in order to point out which project in the decision makers’ opinion is more advantageous for sustainable urban development. The identical rank was made up from the existing values and successfully applied in similar decision-making problems: Fuzzy AHP, Fuzzy TOPSIS, NEAT F-PROMETHEE I, NEAT F-PROMETHEE II. The objective was to compare the results achieved by means of the new method and the results obtained by means of known and used methods in the past in assisting multicriteria decisions, in which the decision maker had to make a choice out of many variants, where the criteria were not often quantified.
The performed study showed that the presented PVM-VSI method allows use of it in solving decision problems in which many variants are subject to evaluation with many criteria considered. According to the rank obtained in the new method applied, the best project in the pool of projects submitted to the Citizen Budget is project A3—improvement of the urban bicycle infrastructure. This project was followed in the rank by: A5—pro-eco revitalization of Słowiański Park; A1—construction of a walking path along the river Warta from the East Boulevard to the Lubuski Bridge; A4—integrative playground for handicapped children; and A2—a swimming pool within the river Warta water current. Accounting for urban sustainable development, citizens can be introduced to the obtained rank so that they are aware which of the projects is recommended by experts as best serving the interests of their town.
What this paper highlights is that the new method, when applied, produces final results close to currently used methods, with a view to comparing the outcome when those methods are used in similar decision problems. In this study, project A3 proved to be the best irrespective of the used method. Also, irrespective of the applied method, the final position was taken by project A2. The proposed PVM-VSI method—as demonstrated—has extra merit. It is possible to analyze the consistency of the solution on the grounds of the standard deviation value. The decision maker has the possibility of pointing out those variants that are well defined in the rank and characterized by having the lowest deviation or the smallest variability or inconsistency of the evaluation scores. This method can play a significant role in the decision-making of problems of urban management, or more broadly, sustainable management. In such problems, we often have to deal with imprecise and subjective assessments, expressed on qualitative scales. Meanwhile, the PVM-VSI method we developed takes into account such imprecise and inconsistent assessments, at the same time examining the degree of imprecision and taking it into account in the final results. This is a completely different approach to, for example, the AHP method, in which if there is an inconsistency ratio greater than 0.1 for the examined pairwise comparison matrix, the decision maker must reassess the variants.