𝜃 free (19)
The objective function (14) minimizes the
proportional reduction of the minimized objective
functions obtained by solution 𝑗
. Constraint (15)
establishes that the proportional reduction of the
minimized objective functions obtained by solution
𝑗
must be greater or equal than the composed target
in the efficient frontier (left hand of the constraint).
Constraints (16) estimates that the maximized
objective functions obtained by solution 𝑗
must be
lower or equal than the composed target in the
efficient frontier (left hand of the constraint).
Constraint (17) imposes the convexity of the efficient
frontier, which is associated to the variable returns to
scale (Banker et al., 1984). Constraints (18) and (19)
establish the nature of the decision variables.
In the SE-DEA model
, 𝛿
corresponds to the
efficiency score of the evaluated solution 𝑗
. This
efficiency score, differently from a traditional BCC
input-oriented model (Banker et al., 1984), could
achieve values greater than one or even the model
could be infeasible. The necessary and sufficient
conditions for infeasibility of SE-DEA models when
variable returns to scale are considered (constraint
17), are presented in the study of Seiford & Zhu
(1999). Consequently, a solution 𝑗
that is an extreme
point of the Pareto efficient frontier will have a
𝛿
value greater than one or the associated model could
be infeasible.
In the following sub-section, the performance
metrics for evaluating MOLP solution methods and
the steps for implementing them using the formulated
DEA models are described.
2.2 Performance Metrics for
Evaluating MOLP Solution
Methods
As mentioned previously, the considered categories
for evaluating MOLP solution methods are
cardinality, accuracy, and diversity. The proposed
metrics in every category and the steps for calculating
them are presented as follows.
2.2.1 Cardinality Metric - CM
The cardinality metric (CM) represents the
domination degree of the solutions obtained by a
MOLP method. For this reason, it is a unary metric,
using the information of a unique solution set. In this
study, it is calculated using the INT-SBM model,
where data of all the solutions
𝑆
obtained by a
solution method are evaluated. It is important to
highlight that the dominated and non-dominated
solutions obtained by a solution method are
considered as observed data of the model. The
following steps must be carried out for obtaining the
cardinality metric CM.
Step 1: Execute the INT-SBM model for every
solution of set 𝑆. In this step, a vector Ξ is obtained,
which corresponds to the vector of 𝜉
, the efficient
measure of the INT-SBM model for every solution i
of the set 𝑆.
Step 2: Calculate the efficiency average of vector Ξ.
This value will correspond to the cardinality metric
CM.
The cardinality metric CM is greater than zero,
and lower than or equal to one. A value equal to one
means that it does not exist any solution dominated
by other in the set 𝑆. On the other hand, a value close
to zero means that few non-dominated solutions exist
in the set 𝑆.
2.2.2 Accuracy Metric - AC
The accuracy metric (AC) represents the domination
degree of one MOLP solution method over other
MOLP solution method. Furthermore, it is a binary
metric because it needs two sets of non-dominated
solutions for making the comparison. In this study,
for estimating the accuracy metric AC, the INT-SBM
model and the metafrontier approach, proposed by
O’Donnell et al. (2008), are used together. The
metafrontier approach allows classifying the non-
dominated solutions into different groups. In this
way, two sets of non-dominated solutions, 𝑆
and 𝑆
,
obtained by two different solution methods, are
compared. The following steps must be carried out for
estimating the proposed accuracy metric AC.
Step 1: Execute the INT-SBM model for every non-
dominated solution of set 𝑆
. In this step, a vector Ξ
is obtained, which corresponds to the vector of 𝜉
,
the efficient measure of the INT-SBM model for
every non-dominated solution i of the set 𝑆
.
Step 2: Execute the INT-SBM model for every non-
dominated solution of set 𝑆
. In this step, a vector Ξ
is obtained, which corresponds to the vector of 𝜉
,
the efficient measure of the INT-SBM model for
every non-dominated solution i of the set 𝑆
.
Step 3: Execute the INT-SBM model for every
solution belonging to the union of sets 𝑆
and 𝑆
. In
this step, a vector Ξ
is obtained, which corresponds
to the vector of 𝜉
, the efficient measure of the INT-