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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Benchmark analysis of black-box local explanation methods</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Francesca Naretto</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Francesco Bodria</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Fosca Giannotti</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Dino Pedreschi</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Scuola Normale Superiore</institution>
          ,
          <addr-line>P.za dei Cavalieri, 7, 56126, Pisa, PI</addr-line>
          ,
          <country country="IT">Italy</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>University of Pisa, Largo Bruno Pontecorvo</institution>
          ,
          <addr-line>3, 56127, Pisa, PI</addr-line>
          ,
          <country country="IT">Italy</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>In recent years, Explainable AI (XAI) has seen increasing interest: new theoretical approaches and libraries providing computationally eficient explanation algorithms are proposed daily. Given the increasing number of algorithms, as well as the fact that there is a lack of standardized evaluation metrics, it is dificult to evaluate the goodness of explanation methods from a quantitative point of view. In this paper, we propose a benchmark of explanation methods. In particular, we focused on post-hoc methods that produce explanations of a black-box. We target our analysis for most used XAI methods. Using the metrics proposed in the literature, we quantitatively compare diferent explanation methods categorizing them with respect to the type of data required in input and the type of explanation output.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Explainable AI</kwd>
        <kwd>Machine learning</kwd>
        <kwd>post-hoc local explanation</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Artificial intelligence (AI) systems have been used everywhere for the past few years. This is
due to their impressive performance, achieved by adopting complex Machine Learning (ML)
models that “hide" the logic of their internal processes. For this reason, such models are often
referred to as “black-box models” [
        <xref ref-type="bibr" rid="ref1">1, 2, 3</xref>
        ]. Their opacity may hide potential problems inherited
from training on biased or incorrect data [4]. Thus, there is a substantial risk that relying on
opaque models may lead us to make decisions we do not fully understand or violate ethical
principles. Companies are increasingly incorporating ML models into their AI products and
applications, incurring a potential loss of confidence and trust [ 5]. These risks are particularly
relevant in high-risk decision-making scenarios, such as medicine and finance. For these reasons,
Explainable AI methods have been proposed in recent years: they aim to explain the reasons
that led the ML model to that particular prediction.
      </p>
      <p>Along with them, there has also arisen an urgency to evaluate them, to understand the
pros and cons of various explanations and in what contexts they should be used. Hence, new
metrics are proposed every day. Despite this, the literature still lacks systematic analysis of
explainers, combining diferent types of metrics and allowing for an overview. Therefore, this
article presents an in-depth analysis of the most popular explanation methods both for tabular
data and for images, making a quantitative assessment by taking advantage of the metrics
in the literature. Section 2 present the related works in the literature. In section 3 we will
describe the XAI methods analyzed and the metrics used. Section 4 describes the methodology
used to compare the methods and produce the experiments presented in Section 5. Finally the
conclusions are reported in Section 6. ti</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>The widespread need for XAI in recent years has caused an explosion of interest in the design of
explanation methods and consequently an increase in surveys about them. Several books have
been published [6, 7] detailing the best-known methodologies for making general ML models
interpretable and for explaining the results of machine learning models [7]. There is no clear
view in the literature on how to classify explanation methods. Some works [8, 9] focus their
analysis on the type of data the XAI algorithm can use. Other works [10, 11, 12], on the other
hand, have focused on only one type of explanation.</p>
      <p>However, only a few papers have attempted to compare the explanations analyzed and often
only qualitatively. Evaluating an explanation objectively is not an easy task, as the goodness of
an explanation can sometimes vary from subject to subject. A good explanation should follow
the criteria of fidelity, stability and accuracy [ 13, 14]. Fidelity [15, 16] aims to assess how good
the explainer is at imitating black-box decisions. Several works have pointed out that most
explainer methods are not robust and therefore undermining their applicability in safety-risk
applications [17, 18]. Therefore, another important property of explanations is stability [16, 19]:
we want the explanation not to change for successive runs with the same parameters and
we also want it to be stable for small perturbations of the input. Finally, we can measure the
accuracy [20, 21] of the explanation, i.e., how well the explanation revealed the aspects of the
data that are efectively the most relevant for the black-box decision.</p>
    </sec>
    <sec id="sec-3">
      <title>3. Background</title>
      <p>In this section we present the building blocks necessary for the quantitative assessment of the
explanations. Firstly, in Section 3.1, we present the diferent explanation methods to use for
providing explanations. Then, in Section 3.2 we present a brief overview of the metrics available
in the literature for evaluating the explanations.</p>
      <sec id="sec-3-1">
        <title>3.1. Explainers</title>
        <p>
          Because of the multitude of explanatory methods in the literature, we briefly present a taxonomy
of methods [
          <xref ref-type="bibr" rid="ref1">1, 22</xref>
          ] to allow the reader understanding the proposed categorization of explanatory
methods. In a first step, we distinguish between interpretable-by-design methods from
posthoc methods. The goal of the former is to build an inherently transparent model, while the
latter seek to provide explanations for an external black-box model. The second diferentiation
distinguishes explainers methods into global and local. Global methods aim to explain the
overall logic of a black-box model, while local methods focus on explaining a prediction for
specific instances. In this paper, we focus on local post-hoc methods because they can be easily
compared using existing metrics in the literature. We selected the most popular explainers with
a working Python implementation available.
        </p>
        <p>Tabular data We focus our analysis on the feature importance and rule explanation methods
since these are the most popular explanations for tabular data. To allow a better comparison,
we selected 5 methods that exploit diferent processes to construct an explanation.</p>
        <p>LIME [23], is a local model agnostic method in which the explanation is derived locally from
records generated randomly in the neighborhood of the instance  to explain. lime samples
instances both in the vicinity of  (with a high weight) and far away from  (low weight) to
approximate the decision boundary in proximity of the instance to explain but still capturing
diferent types of instances. These generated samples are then used to train a sparse linear
model (e.g. a surrogate model, ) whose weights are the local feature importance consists of the
weights of the sparse linear model.</p>
        <p>SHAP [24], is a method for computing approximated Shapley values [25], a concept from game
theory, and use them as explanation.The shapley value of a feature represents the contribution
of that feature to the final prediction of the black-box. shap is an additive feature attribution
method and respect the following definition: 0 + ∑︀ =1 , where  ∈ R are efects assigned
to each feature,  is the number of input features, and 0 is the value of the prediction if all
the features are removed. We consider the KernelExplainer: an agnostic approach.</p>
        <p>DALEX [26] contains an implementation of a variable attribution approach [27].
Mathematically, it consists of a decomposition of the model’s predictions, in which each decomposition
can be seen as a local gradient and used to identify the contribution of each attribute.</p>
        <p>ANCHOR [28] is a model-agnostic explainer that outputs rules, called anchors. An anchor
has the same structure of a rule with the characteristic that for decisions in which the anchor is
valid, changes in the values of other instance features do not change the result.</p>
        <p>LORE [15], is a method, similar to lime, that provides faithful explanations exploiting a
genetic algorithm for creating the neighborhood of the record to explain. After the creation of
the synthetic samples, it retrieves an explanation composed of a decision rule, that corresponds
to the path on a learned decision tree followed by the instance  to reach the decision  and a
set of counterfactual rules, which have a diferent classification w.r.t. .</p>
        <p>We choose lime and anchor, which are two of the fastest explanation methods available in
the literature due to the random generation of the neighborhood. However, this randomicity
does, by construction, also afect the explanation’s stability and validity. To check this expected
behavior, we also considered lore. This method exploits a genetic algorithm to create the
synthetic neighborhood. Hence we expect greater stability w.r.t. lime and anchor. shap is a
very popular explanation method based on a completely diferent approach compared to the
ones just mentioned. However, for non linear methods, shap performs an approximation, hence
it is important to validate the goodness of the explanation in this setting. Also dalex exploits
diferent approximations, hence this is the reason why we considered this last method.
Image data For image data we compared the most well known attribution mechanism called
saliency maps. A Saliency Map method assign to every pixel of an image a score representing
how important the pixel is to the prediction. There are two approaches to producing saliency
maps: segmentation-based methods and pixel-based methods. The former, first segment the
image and assign each portion a single value, while the latter assign a value for each pixel.
Pixel-wise methods are more common and the most popular approaches are:</p>
        <p>INTGRAD, Integrated Gradient [29] utilizes the gradients of a black-box along with the
sensitivity techniques of  -lrp. Given the black-box , the instance to explain , and let ′ be
the baseline input1. intgrad constructs a path, varying opacity, from ′ to  and computes the
gradients of points along the path. The points are taken by gradually modifying the opacity of
. Integrated gradients are obtained by cumulating the gradients of these points.</p>
        <p>LRP, Layer-wise Relevance Propagation [30] explains the classifier’s decisions by
decomposition.  -lrp redistributes the black-box prediction backward to the input using local redistribution
rules until it assigns a relevance score to each input pixels. The simple  -lrp rule redistributes
relevance from layer  + 1 to layer :  = ∑︀ ∑︀+  where  and is the activation of
the neuron ,  is the weight connecting the neurons of  and  of the two layers and a small
stabilization term  is added to prevent division by zero.</p>
        <p>DEEPLIFT [31], computes saliency maps in a backward fashion similarly to  -lrp, but it
uses a baseline reference like in intgrad. deeplift uses the slope, instead of the gradients,
which describes how the output  = () changes as the input  difers from the baseline ′.
Like  -lrp, an attribution value  is assigned to each layer  of the black-box going backward
from the output .</p>
        <p>SHAP has two variants that can be employed for image classification: deep-shap and
gradshap. deep-shap is a high-speed approximation algorithm for shap values for deep learning
models for images that builds on a connection with deeplift. The implementation difers from
the original deeplift by using as baseline, a distribution of background samples instead of a
single value and it uses Shapley equations to linearise non-linear components of the black-box
such as max, softmax, products, divisions, etc. grad-shap, instead, is based on intgrad and
smoothgrad, presented in the following of this section. As an adaptation to make intgrad
value approximate shap values, grad-shap reformulates the integral as an expectation and
combines that expectation with sampling reference values from the background dataset as done
in smoothgrad.</p>
        <p>Among the segmentation based methods we have lime and xrai.</p>
        <p>LIME can also be used for retrieving feature importance, also supports images lime divides
the input image into segments called superpixels. Then it creates the neighbourhood by randomly
substituting the super-pixels with a uniform, possibly neutral, color.</p>
        <p>XRAI [32] is intgrad augmented with segmentation. xrai iteratively segment the image and
tests each region’s importance using intgrad, fusing smaller regions into larger segments based
on attribution scores. The segmentation is repeated several times to reduce the dependency on
image segmentation algorithm.</p>
        <p>Apart from these two types of methods, there are hybrid approaches that create very coarse
saliency maps that in some parts highlight large clusters of pixels while in others are more
detailed.</p>
        <p>GRAD-CAM [33] uses the gradient information flowing into the last convolutional layer of a</p>
        <sec id="sec-3-1-1">
          <title>1The baseline ′ is generally chosen as a zero matrix. or a black image.</title>
          <p>convolutional neural network to assign saliency values to each neuron for a particular decision.</p>
          <p>GRAD-CAM++ [34] extends grad-cam solving some related issues about robustness. If
multiple objects have slightly diferent orientations or views, diferent feature maps may be
activated with difering spatial footprints. grad-cam++ fix this problem by taking a weighted
average of the pixel gradients.</p>
          <p>
            RISE [20] produces saliency map for an image  using a masking mechanism. rise generates
 random mask  ∈ [
            <xref ref-type="bibr" rid="ref1">0, 1</xref>
            ] from Gaussian noise. The input image  is element-wise multiplied
with these masks , and the result is fed to the black-box. The saliency map is obtained as a
linear combination of the masks with the predictions corresponding to the respective masked
inputs.
          </p>
          <p>SMOOTHGRAD [35] is a diferent type of method which tries to improve the saliency maps
produced by other approaches. Usually, a saliency map is created directly on the gradient of the
model’s output signal w.r.t. the input /. smoothgrad augments this process by smoothing
the gradients.</p>
        </sec>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Metrics</title>
        <p>There are two ways of evaluating explanations: qualitative evaluation, which focuses on the
actual usability of the explanations from the end user’s point of view. The other validation
method is the quantitative method, which is considered for this work. In this case, the evaluation
focuses on the performance of the explainer and how close the explanation method  is to
the black-box model . In this section, we briefly describe the validation metrics used for
bench-marking local post-hoc explainer methods.</p>
        <p>Tabular data For tabular data, one of the metric most used is the fidelity : the objective of this
metric is to measure how good the explanation method is at mimicking the black-box decisions.
In methods where there is a creation of a surrogate model  to mimic , such as lime, the fidelity
is computed with the accuracy of the predictions of  w.r.t.  on the instances used to train
 [15]. For methods without a surrogate model, a very simple model can be created using the
explanation and then the fidelity is computed as the accuracy of such model on the prediction
of the black-box. The closer to one, the better.</p>
        <p>Another measure we considered is the stability: it aims at validating how stable the
explanations are for similar records. The main idea is that, if we have two similar records, also the
explanations should be close. To calculate this metric the Lipschitz constant [19] is exploited:
given a record to explain  and a neighborhood  and ′ composed of instances similar to
, the explanation method  provides explanations  and ′ and the stability is computed:
 = max ‖− ′ ‖ , ∀′ ∈ . Intuitively, the higher the value, the better is the model to
‖− ′‖
present similar explanations for similar inputs.</p>
        <p>
          Other metrics have been proposed [36] with the aim of validating the goodness of explanations
by changing the input record, depending on the explanations. The idea is that it is possible
to validate the correctness of explanations by removing (in order of importance) the features
that the explanation method considers important. The more features removed, the more the
performance of the black-box should degrade. In this work, we consider the faithfulness [19],
which aims at validating whether the importance scores obtained from the explanation method
indicate true importance. Mathematically, given a black-box  and the feature importance 
extracted from an explanation method, the faithfulness removes attributes in order of importance
given by . At each removal, the efect on the performance of  is evaluated and these values
are then employed to compute the overall correlation between feature importance and model
performance. It results in a value range [
          <xref ref-type="bibr" rid="ref1">− 1, 1</xref>
          ]: the higher the value, the better the faithfulness.
        </p>
        <p>We also consider monotonicity that takes the complementary approach w.r.t. faithfulness. It
evaluates the efect of  by incrementally adding each attribute in order of increasing importance.
In an opposite way than before, we expect that the black-box performance increases by adding
more and more features, thereby resulting in monotonically increasing model performance2.
Beside these metrics, during the comparison of diferent explanation methods, standard metrics
like accuracy, precision and recall are also evaluated, as well as the running time.
Image data For image data, a strategy to validate the correctness of the explanation  =
 (, ) is to remove the features that the explanation method  found important and see how
the accuracy of the black-box  degrades. These metrics are called deletion and insertion [20].
The intuition behind deletion is that removing the “cause” will force the black-box to change its
decision. For the computation of the deletion metric, we substitute pixels in order of importance
scores given by the explanation method with black pixels. For the insertion metric, we blurred
the whole image with a Gaussian Kernel and then slowly inserted high definition pixels in
order of importance. For every substitution we made, we query the image to the black-box,
obtaining an accuracy. The final score is obtained by taking the area under the curve (AUC) [ 37]
of accuracy as a function of the percentage of removed pixels. For the deletion metric, the
lower the better, for insertion metric, the highest the better. In Figure 1 we have an example
of this metric computed on the hockey figure of imagenet. We remark that the selection of
substituting the meaningful pixels with black ones is a standard procedure in the literature,
even if this selection may not correspond to the absence of information, which is our goal. To
further check this problem we exploited sensitivity, presented in the following.</p>
        <p>The deletion and insertion metrics compute the accuracy of the explanation method to rank
2An implementation of monotonicity and faithfulness is available in aix360
the most important pixels. However, another important desirable property is the stability of the
explanation, i.e., that the explanation should not change for small perturbations of the input
image. Explanation sensitivity [16] measures the extent of explanation change when the input is
slightly perturbed. The sensitivity metric measures the maximum sensitivity of an explanation
using the Monte Carlo sampling-based approximation. By default, it samples multiple data
points from a subspace of an infinite sphere of predefined radius. Note that the maximum
sensitivity is similar to the Lipschitz [38] continuity metric, however, it is more robust and
easier to estimate for image data.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Benchmarking Settings</title>
      <p>The main focus of this paper is to quantitatively assess the quality of explanations. Each
time a new method is proposed, some of the available metrics are exploited to evaluate the
goodness of the explanations extracted, such as in [15, 26]. In addition, some authors also
propose new metrics along with their methods of explanation. This thus leads to great dificulty
in comparing explanations obtained from diferent explainers. For this reason, we evaluate,
using the same quantitative methodology, the goodness of explanations obtained using the
most popular explainers. To achieve this goal, we compared the explanations, obtained from
the application of diferent explanation methods, considering the diferent metrics present in
the literature. Given a dataset ℒ with labels ℒ, the methodology followed for comparing the
diferent explanations is as follows:
1. Split the dataset ℒ into train and test, obtaining  with its labels  and 
with its labels ;
2. Define and train a black-box model  on the train set  and ;
3. Test the black-box  on the test set , obtaining  = ();
3. Explain , the local predictions of , using an explanation method , obtaining a set
of explanations Exps = (, , ).
4. Depending on the type of input data and on the kind of explanation provided, apply the
metrics available.</p>
      <p>To compare the performance of the metrics, we adapted the Nemenyi test. For each dataset, we
record the average ranking of explainers for a given metric and then run the Nemenyi test to
see if one method is statistically better than another.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Experiments</title>
      <p>The aim of this paper is to analyze quantitatively the goodness of the explanations available in
the literature. To do this, the experimentation and validation part is of utmost importance. Below,
we have divided the experiments into several sections, one for each type of data considered: in
Section 5.1, we present the datasets, black-boxes, explanation methods and the metrics used in
the context of tabular data, while in Section 5.2 for images.
lime</p>
      <p>shap
mean and the standard deviation over a subset of 50 test set records.</p>
      <sec id="sec-5-1">
        <title>5.1. Tabular Data</title>
        <p>Dataset For the tabular data we consider three benchmark datasets: all of them have diferent
characteristics that may afect the performance of the explanation methods. For all of them, we
apply a standard pre-process: we replaced the categorical variables using a TargetEncoder, we
replaced the missing values using the mean (of median) of the column under analysis, and we
removed the outliers by visualizing the statistical distribution of the variables. We analyzed
adult3: a binary classification with the task of predicting if a person earns more or less than
50K per year. It has 14 attributes (numerical and categorical) and 48842 records. Then, we
considered german4: a binary classification for predicting the credit risk of a person. It has 20
attributes, mostly categorical, with 1000 records. Lastly, compas-m5: a multi-class dataset, in
which the goal is to predict the recidivism of a convicted person, with 3 classes of risk recidivism.
It has 21800 record and 10 variables, all of them categorical except .</p>
        <p>Black-box</p>
        <p>For comparing the explanations, we define and train 3 ML models, for each dataset:
a Logistic Regression (LG), then XGBoost6 (XGB), and Catboost7 (CAT). The performance of the
black-box models are reported in Table 18.</p>
        <p>Explanation methods For validating the explanations on tabular data, we refer to seven
explanation methods already presented in Section 3. For feature importance we considered</p>
        <sec id="sec-5-1-1">
          <title>3adult: https://archive.ics.uci.edu/ml/datasets/adult</title>
          <p>4german: https://archive.ics.uci.edu/ml/datasets/statlog+(german+credit+data)
5compas-m: https://www.kaggle.com/datasets/danofer/compass
8The dataset was split into train and test with ratio 80% − 20%</p>
          <p>Dataset</p>
          <p>Black-Box
adult</p>
          <p>lime</p>
          <p>shap
lime with 5000 synthetic samples to generate for each record to explain, shap, and dalex with
the break down method.</p>
          <p>Metrics For tabular data we consider the four diferent metrics already presented in Section 3.2:
ifdelity , stability, faithfulness, and monotonicity. The results obtained from the applications of
these metrics are reported in Table 2 for the fidelity and faithfulness, while in Table 3 we report
the stability. The monotonicity is not reported since for every method it was False, showing
that no method is compliant with this requirement.</p>
          <p>Discussion In Figure 2, we report an overall ranking evaluation of the explanation methods
in terms of fidelity and stability. From this plot, we can clearly see that lore and anchor,
which are the rule-based methods, perform better than the feature importance ones. This
result is particularly interesting because feature importance methods are more studied than
logical explanations even though the latter are more similar to human thinking. [8]. Our
experiments show that rule-based methods have very high fidelity, correctly replicating the
black-box behavior. This fact is also highlighted by the results on stability, that are extremely
good for lore, followed by anchor. Regarding the feature importance methods, lime also has
excellent fidelity, but unfortunately this method sufers in terms of stability due to its random</p>
          <p>mnist</p>
          <p>mnist
generation of the neighborhood. shap and dalex, instead, do not exhibit a good fidelity but
are better in terms of stability w.r.t. lime. Finally, in Table 2, we present the faithfulness. shap
achieves the best results, being the metrics with values between − 1 and 1. However, we remark
that none of the methods reached optimality. Nevertheless, shap turns out to be the best in this
context, followed by dalex and lime.</p>
        </sec>
      </sec>
      <sec id="sec-5-2">
        <title>5.2. Image Data</title>
        <p>Dataset For the experiments on images, we considered three datasets. The handwritten
number classification dataset mnist9. It has 10 classes, from 9 to 10, the images are in low
resolution (28x28) and greyscale. Then, cifar10: low resolution (32x32) color images dataset
with 10 classes, ranging from dogs to airplanes. Lastly, imagenet11: composed of high resolution
color images (224x224), with a 1000 classes. We chose these datasets because they are the most
utilized, and we have diferent classes with various image dimensions.</p>
        <p>Black-box On these three datasets, we trained the models most used in literature to evaluate
the explanation methods: for mnist and cifar we trained a convolutional neural network
with two convolutions and two linear layers, while for imagenet we decided to use the VGG16
network [39]. The performance of the black-box models are reported in Table 1.
Explanation methods We tested every method presented in Section 3.1 with the following
specifications. For the lime segmentation we used the quickshift algorithm [40] with a
neigh9http://yann.lecun.com/exdb/mnist/
10http://image-net.org/
11https://www.cs.toronto.edu/~kriz/cifar.html</p>
        <p>mnist
mnist</p>
        <p>Runtime
cifar
2.090 (0.612)
0.089 (0.189)
0.153 (0.357)
0.207 (0.806)
0.131 (0.738)
0.055 (0.010)
1.829 (0.350)
0.310 (0.225)
0.093 (0.592)
0.047 (0.292)
0.501 (0.461)
borhood size of 2000. In intgrad, xrai, and deeplift we used a black image as background.
For deep-shap and grad-shap, 100 images are taken randomly from the training set and used
to approximate the Shapley values. In grad-cam and grad-cam++ the last convolutional layer
was selected from which to calculate the gradients. For the masking of rise, we used 2000 masks
generate randomly.</p>
        <p>Metrics We evaluated the metrics reported in Section 3.2: Deletion/Insertion results are
reported in Table 4 and the Sensitivity results in Table 5.2.</p>
        <p>Discussion For image data the best method in general is rise, however as highlighted from
Figure 3 none of the methods has statistical significance to be considered better than the rest.
All the methods are very noisy and unstable as pointed out from the stability and the high
standard deviation among all the methods in the deletion/insertion metrics. lime and xrai
sufers of stability issues due to the randomness of the segmentation preprocessing. lime is
also the worst method when measuring accuracy. Guided methods like smoothgrad are even
worst than random methods when computing the stability of the explanations. We support
the findings of [ 41] in which they pointed out that guided methods are not good explainers.
smoothgrad is not that bad in high resolution images, but this is caused by the fact that the
guided perturbation plays an inferior role than the gradient computation. In general gradient
approaches like intgrad and deeplift are the best approaches for accuracy, especially when
dealing with high-resolution images. The computation are fast, and stable, even if we compute
the second order gradients like in grad-cam++. intgrad and deeplift are more precise than
grad-cam and grad-cam++ since the saliency maps produced by these last two methods is
coarse and unrefined. shap based methods works only on low resolution images due to the
approximation factor. The higher the resolution the more images you need as background to
better approximate the Shapley values. However in doing this the memory used and the runtime
increase exponentially. rise is the best compromise and can reach high level of accuracy and
stability even if it is based on random masking.</p>
      </sec>
    </sec>
    <sec id="sec-6">
      <title>6. Conclusions</title>
      <p>We proposed a benchmark of explanation methods, taking advantage of metrics proposed in the
literature to compare diferent explanation methods quantitatively. The quantitative analysis
showed that the best-performing explanation methods for tabular data are the rule-based ones,
which have high fidelity and stability, providing explanations faithful to the black-box decisions.
For images, the most stable methods are those based on gradients, while segmentation-based
methods have dificulty because of their random nature. Regarding accuracy, none of the
methods is statistically better than the others; however, the best method in our experiments was
rise. In general, no one method predominated over the others, emphasizing the dificulty of
creating efective and solid explanations at the same time. As a future work we aim at expanding
this analysis considering other data, such as text and time series, as well as other metrics.
Another possibility is to measure the comprehensibility of explanations by doing experiments
directly on humans.</p>
    </sec>
    <sec id="sec-7">
      <title>Acknowledgments</title>
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HumanE-AI Net, ERC-2018-ADG G.A. 834756 XAI: Science and technology for the eXplanation of
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