jmlr jmlr2013 jmlr2013-12 knowledge-graph by maker-knowledge-mining
Source: pdf
Author: Nayyar A. Zaidi, Jesús Cerquides, Mark J. Carman, Geoffrey I. Webb
Abstract: Despite the simplicity of the Naive Bayes classifier, it has continued to perform well against more sophisticated newcomers and has remained, therefore, of great interest to the machine learning community. Of numerous approaches to refining the naive Bayes classifier, attribute weighting has received less attention than it warrants. Most approaches, perhaps influenced by attribute weighting in other machine learning algorithms, use weighting to place more emphasis on highly predictive attributes than those that are less predictive. In this paper, we argue that for naive Bayes attribute weighting should instead be used to alleviate the conditional independence assumption. Based on this premise, we propose a weighted naive Bayes algorithm, called WANBIA, that selects weights to minimize either the negative conditional log likelihood or the mean squared error objective functions. We perform extensive evaluations and find that WANBIA is a competitive alternative to state of the art classifiers like Random Forest, Logistic Regression and A1DE. Keywords: classification, naive Bayes, attribute independence assumption, weighted naive Bayes classification
Reference: text
sentIndex sentText sentNum sentScore
1 Of numerous approaches to refining the naive Bayes classifier, attribute weighting has received less attention than it warrants. [sent-13, score-0.423]
2 Most approaches, perhaps influenced by attribute weighting in other machine learning algorithms, use weighting to place more emphasis on highly predictive attributes than those that are less predictive. [sent-14, score-0.44]
3 In this paper, we argue that for naive Bayes attribute weighting should instead be used to alleviate the conditional independence assumption. [sent-15, score-0.442]
4 Keywords: classification, naive Bayes, attribute independence assumption, weighted naive Bayes classification 1. [sent-18, score-0.515]
5 If there is sufficient data present for every possible combination of attribute values, direct estimation of each relevant multi-variate probability will be reliable. [sent-23, score-0.261]
6 In practice, naive Bayes’ attribute independence assumption is often violated, and as a result its probability estimates are often suboptimal. [sent-33, score-0.39]
7 These methods are aimed at enhancing naive Bayes’ accuracy by relaxing the assumption of conditional independence between attributes given the class label (Langley and Sage, 1994; Friedman and Goldszmidt, 1996; Zheng et al. [sent-37, score-0.204]
8 The second category comprises attribute weighting methods and has received relatively little attention (Hilden and Bjerregaard, 1976; Ferreira et al. [sent-41, score-0.313]
9 There is some evidence that attribute weighting appears to have primarily been viewed as a means of increasing the influence of highly predictive attributes and discounting attributes that have little predictive value. [sent-43, score-0.463]
10 For example, weighting by mutual information between an attribute and the class is directly using a measure of how predictive is each individual attribute (Zhang and Sheng, 2004). [sent-45, score-0.574]
11 In contrast, we argue that the primary value of attribute weighting is its capacity to reduce the impact on prediction accuracy of violations of the assumption of conditional attribute independence. [sent-46, score-0.574]
12 • We present novel algorithms for learning attribute weights for naive Bayes. [sent-50, score-0.4]
13 It should be noted that the motivation of our work differs from most previous attribute weighting methods. [sent-51, score-0.313]
14 We view weighting as a way to reduce the effects of the violations of the attribute independence assumption on which naive Bayes is based. [sent-52, score-0.442]
15 Also, our work differs from semi-naive Bayes methods, as we weight the attributes rather than modifying the structure of naive Bayes. [sent-53, score-0.206]
16 Our novel techniques for learning naive Bayes weights are described in Section 4 where we also discuss their connection with naive Bayes and Logistic Regression in terms of parameter optimization. [sent-58, score-0.249]
17 In the most general case, this weight depends on the attribute value: a ˆ ˆ ˆ P(y, x) = P(y) ∏ P(xi |y)wi,xi . [sent-78, score-0.282]
18 Unless explicitly stated, in this paper we intend the intermediate form when we refer to attribute weighting, as we believe it provides an effective trade-off between computational complexity and inductive power. [sent-83, score-0.261]
19 Appropriate weights can reduce the error that results from violations of naive Bayes’ conditional attribute independence assumption. [sent-84, score-0.419]
20 Attribute weighting is strictly more powerful than attribute selection, as it is possible to obtain identical results to attribute selection by setting the weights of selected attributes to 1. [sent-93, score-0.678]
21 0, and assignment of other weights can create classifiers that cannot be expressed using attribute selection. [sent-95, score-0.29]
22 1 Dealing with Dependent Attributes by Weighting: A Simple Example This example shows the relative performance of naive Bayes and weighted naive Bayes as we vary the conditional dependence between attributes. [sent-97, score-0.235]
23 In particular it demonstrates how optimal assignment of weights will never result in higher error than attribute selection or standard naive Bayes, and that for certain violations of the attribute independence assumption it can result in lower error than either. [sent-98, score-0.68]
24 For each of the 4 possible attribute value combinations (x1 , x2 ) ∈ {(0, 0), (0, 1), (1, 0), (1, 1)}, we selected values for the class probability given the attribute value combination from the set: P(y|x1 , x2 ) ∈ {0. [sent-103, score-0.522]
25 We then set the values for the attribute value probabilities P(x1 , x2 ) by fixing the marginal distributions to a half P(x1 ) = P(x2 ) = 1/2, and varying the correlation between the attributes using 1950 A LLEVIATING NB ATTRIBUTE I NDEPENDENCE A SSUMPTION BY ATTRIBUTE W EIGHTING 0. [sent-107, score-0.336]
26 7 Figure 1: Variation of Error of naive Bayes, selective naive Bayes, weighted naive Bayes and classifier based only on prior probabilities of the class as a function of conditional dependence (conditional mutual information) between the two attributes. [sent-124, score-0.368]
27 P(X1 = 0, X2 = 0) = P(X1 = 1, X2 = 1) = Note that when ρ=−1 the attributes are perfectly anti-correlated (x1 =¬x2 ), when ρ=0 the attributes are independent (since the joint distribution P(x1 , x2 ) is uniform) and when ρ = 1 the attributes are perfectly correlated. [sent-126, score-0.225]
28 It can be seen that when conditional mutual information (CMI) is small, naive Bayes performs better than selective naive Bayes and the prior classifier. [sent-152, score-0.243]
29 As CMI is increased, naive Bayes performance deteriorates compared to selective naive Bayes. [sent-155, score-0.243]
30 We have shown that weighted naive Bayes is capable of expressing more accurate classifiers than selective naive Bayes. [sent-159, score-0.258]
31 Langley and Sage (1994) proposed the Selective Bayes (SB) classifier, using feature selection to accommodate redundant attributes in the prediction process and to augment naive Bayes with the ability to exclude attributes that introduce dependencies. [sent-170, score-0.26]
32 The technique is based on searching through the entire space of all attribute subsets. [sent-171, score-0.261]
33 On each iteration, the method considers adding each unused attribute to the subset on a trial basis and measures the performance of the resulting classifier on the training data. [sent-174, score-0.261]
34 The attribute that most improves the accuracy is permanently added to the subset. [sent-175, score-0.261]
35 The algorithm terminates when addition of any attribute results in reduced accuracy, at which point it returns the list of current attributes along with their ranks. [sent-176, score-0.336]
36 The rank of the attribute is based on the order in which they are added to the subset. [sent-177, score-0.261]
37 Similar to Langley and Sage (1994), Correlation-based Feature Selection (CFS) used a correlation measure as a metric to determine the relevance of the attribute subset (Hall, 2000). [sent-178, score-0.261]
38 The Selective Bayesian Classifier (SBC) of Ratanamahatana and Gunopulos (2003) also employs decision trees for attribute selection for naive Bayes. [sent-189, score-0.388]
39 Only those attributes appearing in the top three levels of a decision tree are selected for inclusion in naive Bayes. [sent-190, score-0.202]
40 Naive Bayes is trained on an attribute set which comprises the union of attributes appearing in all five decision trees. [sent-193, score-0.353]
41 This strategy uses a single weight and therefore is not strictly performing attribute weighting. [sent-195, score-0.282]
42 Their approach is motivated as a means of alleviating the effects of violations of the attribute independence assumption. [sent-196, score-0.28]
43 Zhang and Sheng (2004) used the gain ratio of an attribute with the class labels as its weight. [sent-206, score-0.261]
44 The gain ratio is a well-studied attribute weighting technique and is generally used for splitting nodes in decision trees (Duda et al. [sent-208, score-0.33]
45 The weight of each attribute is set to the gain ratio of the attribute relative to the average gain ratio across all attributes. [sent-210, score-0.543]
46 ∑a GR(i) i=1 (7) The gain ratio of an attribute is then simply the Mutual Information between that attribute and the class label divided by the entropy of that attribute: P(x1 ,y) I(Xi ,Y ) ∑y ∑x1 P(x1 , y) log P(x1 )P(y) . [sent-213, score-0.522]
47 An attribute weighting scheme based on differential evolution algorithms for naive Bayes classification have been proposed in Wu and Cai (2011). [sent-217, score-0.423]
48 First, a population of attribute weight vectors 1953 Z AIDI , C ERQUIDES , C ARMAN AND W EBB is randomly generated, weights in the population are constrained to be between 0 and 1. [sent-218, score-0.311]
49 A scheme used in Hall (2007) is similar in spirit to SBC where the weight assigned to each attribute is inversely proportional to the minimum depth at which they were first tested in an unpruned decision tree. [sent-223, score-0.299]
50 For example, one can assign weight to an attribute i as: wi = 1 T T 1 ∑ √dti . [sent-226, score-0.303]
51 (8) t where dti is the minimum depth at which the attribute i appears in decision tree t, and T is the total number of decision trees generated. [sent-227, score-0.295]
52 To understand whether the improvement in naive Bayes accuracy was due to attribute weighting or selection, a variant of the above approach was also proposed where all non-zero weights are set to one. [sent-228, score-0.452]
53 For example, the weight of an attribute i can be defined as: 1 wi = √ . [sent-232, score-0.303]
54 (2001) is the only one to use Equation 4, weighting each attribute value rather than each attribute. [sent-235, score-0.313]
55 They used entropy-based discretization for numeric attributes and assigned a weight to each partition (value) of the attribute that is proportional to its predictive capability of the class. [sent-236, score-0.357]
56 In that case the weight of for value j of the attribute i can be written as: wi j ∝ 1 ∑ | P(y|Xi = j) − |Y | | 1/α α . [sent-242, score-0.303]
57 y where P(y|Xi = j) denotes the probability that the class is y given that the i-th attribute of a data point has value j. [sent-243, score-0.261]
58 Alternatively, the baseline class distribution can be set to the class probabilities across all values of the attribute (i. [sent-244, score-0.261]
59 A LLEVIATING NB ATTRIBUTE I NDEPENDENCE A SSUMPTION BY ATTRIBUTE W EIGHTING where P(y|Xi = miss) is the class prior probability across all data points for which the attribute i is not missing. [sent-248, score-0.261]
60 Many researchers have investigated techniques for extending the basic naive Bayes independence model with a small number of additional dependencies between attributes in order to improve classification performance (Zheng and Webb, 2000). [sent-251, score-0.204]
61 In this paper we are interested in improving performance of the NB classifier by reducing the effect of attribute independence violations through attribute weighting. [sent-263, score-0.541]
62 While it is conceivable that semi-naive Bayes methods and more general Bayesian Network classifier learning could also benefit from attribute weighting, we leave its investigation to future work. [sent-265, score-0.261]
63 1 WANBIA Many previous approaches to attribute weighting for naive Bayes have found weights using some form of mechanism that increases the weights of attributes that are highly predictive of the class and decreases the weights of attributes that are less predictive of the class. [sent-270, score-0.66]
64 Naive Bayes delivers Bayes optimal classification if the attribute independence assumption holds. [sent-272, score-0.28]
65 Weighting should only be applied to remedy violations of the attribute independence assumption. [sent-273, score-0.28]
66 In contrast, a method that uses a measure such as mutual information with the class to weight the attribute will 1955 Z AIDI , C ERQUIDES , C ARMAN AND W EBB Name NB GRW SBC MH SB CFS SBC-FS MH-FS FNB-d1 FNB-d2 AnDE TAN RF LR WANBIACLL WANBIAMSE Description Naive Bayes. [sent-278, score-0.282]
67 Use gain ratio as attribute weights in naive Bayes, shown in Equation 7 (Zhang and Sheng, 2004). [sent-281, score-0.4]
68 Assign weight to attribute i as given in Equation 8 where L = 5 with a bootstrap size of 10%. [sent-282, score-0.282]
69 Assign weight to attribute i as given in Equation 8 where L = 10 with a bootstrap size of 50% (Hall, 2007). [sent-284, score-0.282]
70 Weights computed per attribute value using Equation 10 with α = 2. [sent-292, score-0.261]
71 Weights computed per attribute value using Equation 10 with α = 2. [sent-293, score-0.261]
72 Following from Equations 1, 2 and 5, let us re-define the weighted naive Bayes model as: ˆ P(y|x; π, Θ, w) = πy ∏i θwii=xi |y X w ∑y′ πy′ ∏i θXii=xi |y′ , (10) with constraints: ∑y πy = 1 and ∀y,i ∑ j θXi =xi |y = 1, where • {πy , θXi =xi |y } are naive Bayes parameters. [sent-309, score-0.235]
73 • w is a vector of class-independent weights, wi for each attribute i. [sent-312, score-0.282]
74 1, the naive Bayes (NB) model for estimating P(y|x) is parameterized by a class probability vector π ∈ [0, 1] |Y | and a matrix Θ, consisting of class and attribute dependent probability vectors θi,y ∈ [0, 1]|Xi | . [sent-340, score-0.371]
75 2 PARAMETERS OF W EIGHTED ATTRIBUTE NAIVE BAYES The WANBIA model is an extension of the NB model where we introduce a weight vector w ∈ [0, 1]a containing a class-independent weight wi for each attribute i. [sent-352, score-0.324]
76 Experiments In this section, we compare the performance of our proposed methods WANBIACLL and WANBIAMSE with state of the art classifiers, existing semi-naive Bayes methods and weighted naive Bayes methods based on both attribute selection and attribute weighting. [sent-365, score-0.647]
77 Note that unlike the NB model, the LR model does not require that the domain of attribute values be discrete. [sent-369, score-0.261]
78 Nondiscrete data can also be handled by Naive Bayes models, but a different parameterization for the distribution over attribute values must be used. [sent-370, score-0.261]
79 • Probability Estimates - The base probabilities of each algorithm are estimated using mestimation, since in our initial experiments it leads to more accurate probabilities than Laplace estimation for naive Bayes and weighted naive Bayes. [sent-455, score-0.235]
80 ) + m , (20) where Nxi ,y is the count of data points with attribute value xi and class label y, Ny is the count of data points with class label y, N? [sent-458, score-0.277]
81 Table 5 compares the WDL of naive Bayes in Equation 3 with weighted naive Bayes in Equation 6 as the weight w is varied from 0. [sent-561, score-0.256]
82 5 Single versus Multiple Naive Bayes Weights Learning To study the effect of single versus multiple weight learning for naive Bayes (naive Bayes in Equation 5 versus naive Bayes in Equation 6), we constrained WANBIA to learn only a single weight for all attributes. [sent-853, score-0.262]
83 A1DE relaxes NB’s attribute independence assumption by (only) making each attribute independent given the class and one at1970 A LLEVIATING NB ATTRIBUTE I NDEPENDENCE A SSUMPTION BY ATTRIBUTE W EIGHTING 0−1 Loss 8. [sent-962, score-0.541]
84 As A1DE is based on learning without search, every attribute takes a turn to be a super-parent. [sent-1020, score-0.261]
85 a i=1 Similarly, TAN augments the naive Bayes structure by allowing each attribute to depend on at most one non-class attribute. [sent-1022, score-0.371]
86 The estimate is: a ˆ ˆ ˆ P(y, x) = P(y) ∏ P(xi |y, π(xi )), i=1 where π(xi ) is the parent of attribute xi . [sent-1024, score-0.277]
87 This performance gain is attributed to the fact that WANBIA successfully alleviates the conditional attribute independence assumption. [sent-1155, score-0.28]
88 • WANBIA has significantly better 0-1 loss, RMSE, bias and variance than most existing weighted naive Bayes schemes based on attribute selection and attribute weighting. [sent-1158, score-0.694]
89 As a result, WANBIA sets a new standard for attribute weighing for naive Bayes. [sent-1159, score-0.371]
90 However, it is credible that WANBIA’s strategy for alleviating NB’s attribute independence assumption is complementary to A1DE and TAN, allowing both to be applied to obtain even better classification accuracy. [sent-1162, score-0.28]
91 Our work has been primarily motivated by the observation that naive Bayes conditional attribute independence assumption is often violated and, therefore, it is useful to alleviate it. [sent-1169, score-0.39]
92 We build an argument that in current research, weighting in naive Bayes has been viewed as a way of enhancing the impact of attributes that are highly correlated with the class. [sent-1170, score-0.237]
93 We argue that weighting provides a natural framework for alleviating the attribute independence assumption. [sent-1171, score-0.332]
94 Our two proposed naive Bayes weighting methods WANBIACLL and WANBIAMSE fix naive Bayes’ parameters to be the MAP estimates and learn weights by maximizing conditional log-likelihood and minimizing Mean Square Error respectively. [sent-1172, score-0.301]
95 In interpreting the results presented in this work, it is important to keep in mind that attribute weighting and semi-naive Bayesian relaxation of the attribute independence assumption are mutually compatible. [sent-1178, score-0.593]
96 It remains a direction for future research to explore techniques for attribute weighting in the context of semi-naive Bayes classifiers. [sent-1179, score-0.313]
97 A next step will be to learn a weight for each attribute value per class and a weight for the prior probabilities. [sent-1182, score-0.303]
98 For example, for i-th attribute and y-th class, weight term constitutes βi,y for LR and wi log θxi |y for WANBIA. [sent-1184, score-0.303]
99 A decision tree-based attribute weighting filter for naive Bayes. [sent-4917, score-0.44]
100 Attribute weighting via differential evolution algorithm for attribute weighted naive Bayes (wnb). [sent-5010, score-0.438]
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For instance, the popular Weka toolkit (Hall et al., 2009) emphasizes ease of use but scales poorly; the distributed Apache Mahout library offers scalability at a cost of higher overhead (such as clusters and powerful servers often unavailable to the average user). Also, few libraries offer breadth; for instance, libsvm (Chang and Lin, 2011) and the Tilburg MemoryBased Learner (TiMBL) are highly scalable and accessible yet each offer only a single method. MLPACK, intended to be the machine learning analog to the general-purpose LAPACK linear algebra library, aims to combine efficiency and accessibility. Written in C++, MLPACK uses the highly efficient Armadillo matrix library (Sanderson, 2010) and is freely available under the GNU Lesser General Public License (LGPL). Through the use of C++ templates, MLPACK both eliminates unnecessary copying of data sets and performs expression optimizations unavailable in other languages. Also, MLPACK is, to our knowledge, unique among existing libraries in using generic programming features of C++ to allow customization of the available machine learning methods without incurring performance penalties. c 2013 Ryan R. Curtin, James R. Cline, N. P. Slagle, William B. March, Parikshit Ram, Nishant A. Mehta and Alexander G. Gray. C URTIN , C LINE , S LAGLE , M ARCH , R AM , M EHTA AND G RAY In addition, users ranging from students to experts should find the consistent, intuitive interface of MLPACK to be highly accessible. Finally, the source code provides references and comprehensive documentation. Four major goals of the development team of MLPACK are • • • • to implement scalable, fast machine learning algorithms, to design an intuitive, consistent, and simple API for non-expert users, to implement a variety of machine learning methods, and to provide cutting-edge machine learning algorithms unavailable elsewhere. This paper offers both an introduction to the simple and extensible API and a glimpse of the superior performance of the library. 2. Package Overview Each algorithm available in MLPACK features both a set of C++ library functions and a standalone command-line executable. Version 1.0.3 includes the following methods: • • • • • • • • • • • • • • nearest/furthest neighbor search with cover trees or kd-trees (k-nearest-neighbors) range search with cover trees or kd-trees Gaussian mixture models (GMMs) hidden Markov models (HMMs) LARS / Lasso regression k-means clustering fast hierarchical clustering (Euclidean MST calculation)1 (March et al., 2010) kernel PCA (and regular PCA) local coordinate coding1 (Yu et al., 2009) sparse coding using dictionary learning RADICAL (Robust, Accurate, Direct ICA aLgorithm) (Learned-Miller and Fisher, 2003) maximum variance unfolding (MVU) via LRSDP1 (Burer and Monteiro, 2003) the naive Bayes classifier density estimation trees1 (Ram and Gray, 2011) The development team manages MLPACK with Subversion and the Trac bug reporting system, allowing easy downloads and simple bug reporting. The entire development process is transparent, so any interested user can easily contribute to the library. MLPACK can compile from source on Linux, Mac OS, and Windows; currently, different Linux distributions are reviewing MLPACK for inclusion in their package managers, which will allow users to install MLPACK without needing to compile from source. 3. A Consistent, Simple API MLPACK features a highly accessible API, both in style (such as consistent naming schemes and coding conventions) and ease of use (such as templated defaults), as well as stringent documentation standards. Consequently, a new user can execute algorithms out-of-the-box often with little or no adjustment to parameters, while the seasoned expert can expect extreme flexibility in algorithmic 1. This algorithm is not available in any other comparable software package. 802 MLPACK: A S CALABLE C++ M ACHINE L EARNING L IBRARY Data Set wine cloud wine-qual isolet miniboone yp-msd corel covtype mnist randu MLPACK 0.0003 0.0069 0.0290 13.0197 20.2045 5430.0478 4.9716 14.3449 2719.8087 1020.9142 Weka 0.0621 0.1174 0.8868 213.4735 216.1469 >9000.0000 14.4264 45.9912 >9000.0000 2665.0921 Shogun 0.0277 0.5000 4.3617 37.6190 2351.4637 >9000.0000 555.9600 >9000.0000 3536.4477 >9000.0000 MATLAB 0.0021 0.0210 0.6465 46.9518 1088.1127 >9000.0000 60.8496 >9000.0000 4838.6747 1679.2893 mlpy 0.0025 0.3520 4.0431 52.0437 3219.2696 >9000.0000 209.5056 >9000.0000 5192.3586 >9000.0000 sklearn 0.0008 0.0192 0.1668 46.8016 714.2385 >9000.0000 160.4597 651.6259 5363.9650 8780.0176 Table 1: k-NN benchmarks (in seconds). Data Set UCI Name Size wine Wine 178x13 cloud Cloud 2048x10 wine-qual Wine Quality 6497x11 isolet ISOLET 7797x617 miniboone MiniBooNE 130064x50 Data Set UCI Name Size yp-msd YearPredictionMSD 515345x90 corel Corel 37749x32 covtype Covertype 581082x54 mnist N/A 70000x784 randu N/A 1000000x10 Table 2: Benchmark data set sizes. tuning. For example, the following line initializes an object which will perform the standard kmeans clustering in Euclidean space: KMeans
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