A SURVEY PAPER ON MISSING DATA IN DATA MINING
Missing data are characterized as a portion of the qualities in the data set are either lost or not watched or not accessible because of natural or non natural reasons. Data with missing qualities confuses both the data examination and the accommodation of an answer for new data. Numerous specialists are working on this issue to present more modern techniques. Despite the fact that numerous strategies are available, investigators are confronting trouble in seeking an appropriate technique because of absence of information about the strategies and their applicability. This research paper additionally directs a formal review of the missing data strategy. It talks about the strategies that are analyzed in the written works and perceptions that the authors have made. INTRODUCTION A large portion of this present datasets experience suffers from the issue of missing data. It might lead information mining examiners to end with wrong inferences about data under review. Data mining is the process which provides a concept to attract attention of users due to high availability of huge amount of data and need to convert such data into useful information. Data preparation is a principal phase of data investigation[5][7] Three types of mean imputation methods presented on missing data [1] Rubin investigated about inference and missing data and multiple imputation for non reaction in the overview[3] Allison explored estimates of linear models with incomplete data and on missing data[4] Myrtveit et al. connected missing data strategies to a software project data set, and assessed four missing data procedure are list wise deletion (LD) mean imputation (MI) similar response pattern imputation (SRPI) and full information maximum likelihood (FIML)[11].Junninen et al. evaluated and compared univariate and multivariate methods for missing data imputation in air quality data sets[18] Types of Incomplete Data are little and Rubin characterize a list of missing mechanisms, which are generally acknowledged by the community. There are three mechanisms under which missing data can happen [3] 1) Missing completely at random (MCAR) MCAR is the probability that a observation (Xi) is missing, is unrelated to the estimation of Xi or to the estimation of some other variable and the explanation behind missing is completely random. This circumstance is uncommon in real world and is generally talked about in statistical theory. 2) Missing at random (MAR) MAR is the probability of the observed missingness design, given the observed and unobserved data, does not depend on the values of the unobserved NOVATEUR PUBLICATIONS INTERNATIONAL JOURNAL OF INNOVATIONS IN ENGINEERING RESEARCH AND TECHNOLOGY [IJIERT] ISSN: 2394 3696 VOLUME 3, ISSUE 12, Dec. 2016 46 P a g e data. This component is normal in practice and is normally considered as the default kind of missing data. 3) Not missing at random (NMAR) If the probability that an observation is missing depends on information that is not observed, this kind of missing data is called not missing at random. This circumstance is generally confused and there is no universal solution. REVIEW OF TECHNIQUES FOR MISSING DATA: Four Common missing value methods for dealing with missing values [3] 1. Removing the tuples: If a missing value transpires on any of the factors in the data, eliminate the entire observation. 2. Filling the missing value manually: This strategy is time consuming and not plausible for a vast information set with many missing values. 3. Use global constant: Replace all missing attribute values by a similar consistent, for example, a lable "unknown "or 4. Use the attribute mean value: Filling in the missing estimations of a variable. Substitution with a measure of central tendency, Mean, Median, Midrange, (Max Min)/2 and Mode. Figure 1: Types of missing data technique There are several strategies for treating missing data, a few techniques are described below. Missing data treatment techniques can be isolated into three classes, as proposed in [6] 1.1 MISSING DATA IGNORING TECHNIQUES Listwise deletion (or complete case analysis) If a case has missing data for any of the variables, then essentially avoid that case from the analysis. It is typically the default in statistical packages[19] PAIRWISE DELETION (PD) is referred to as the available case method. This technique considers every feature independently. For each feature, all recorded values in each observation are considered [12] and missing data are overlooked. NOVATEUR PUBLICATIONS INTERNATIONAL JOURNAL OF INNOVATIONS IN ENGINEERING RESEARCH AND TECHNOLOGY [IJIERT] ISSN: 2394 3696 VOLUME 3, ISSUE 12, Dec. 2016 47 P a g e Table 1: overview of ignoring and discarding method Methods Remark Listwise deletion (or complete case analysis) Deletion of all cases containing missing values. High Loss of information Pairwise deletion (PD) Deletion of records only from column containing missing values. Less loss of information by keeping all available values. 1.2 MISSING DATA IMPUTATION TECHNIQUES Imputation method is a class of techniques that expects to fill in the missing values with estimated ones. The goal is to employ known connections that can be distinguished in the valid values of the data set assist in estimating the missing values. This field focuses on imputation of missing data. MEAN VALUE IMPUTATION METHOD: Mean imputation method is one of the most frequently used methods [3] It comprises of replacing the missing data for a given component or attribute by the mean of all known values of that attribute in the class where the instance with missing attribute belongs. HOT DECK IMPUTATION(HD) Given an incomplete pattern, HD replaces the missing data with values form input data vector that is nearest in terms of the attributes that are Known in both patterns. HD attempts to protect the distribution by substituting different observed values for each missing .The similar method of HD is Cold deck imputation method which takes other data source than current dataset[13] K NEAREST NEIGHBOR IMPUTATION (KNN) This strategy uses knearest neighbor algorithms to estimate and replace missing data. The main advantages of this strategy are a) it can estimate both qualitative attributes and quantitative attributes; b) It is not important to construct a predictive model for each attribute with missing data [15] K MEANS CLUSTERING METHOD: K Means is to classify or to group the objects based on attributes/features into k number of group [15] [16] The grouping is finished by minimizing the sum of squares of distances between data and the corresponding cluster centroid.It provides quick and precise way of estimating missing values. FUZZY K MEANS CLUSTERING IMPUTATION (FKMI) In FKMI, membership function plays an important role. Membership function is allocated with every data object that depicts in what degree the data object is belonging to the particular cluster. Data objects would not get allotted to concrete cluster which is indicated by centroid of cluster (as in the case of K means) this is because of the various membership degrees of every data with entire K clusters[17] REGRESSION IMPUTATION: Using regression method for imputation, the values from the features are observed and then predicted values are used for filling Missing values [14] MULTIPLE IMPUTATIONS: The imputed values are draws from a distribution, so they inherently contain some variation. Thus, multiple imputations (MI) illuminates the limitations of single imputation by presenting an additional form of error based on variation in the parameter estimates across the imputation, which is called between imputation error. It NOVATEUR PUBLICATIONS INTERNATIONAL JOURNAL OF INNOVATIONS IN ENGINEERING RESEARCH AND TECHNOLOGY [IJIERT] ISSN: 2394 3696 VOLUME 3, ISSUE 12, Dec. 2016 48 P a g e replaces each missing item with two or more acceptable values, representing a distribution of possibilities [4] Table 2: overview of imputation method Methods Remarks Mean Value imputation Method Replace MVs with the mean of Resultant data. Mean and SD after imputation may be much higher than that of original. Hotdeck (HD) Imputation each missing value is replaced with an observed response from a "similar" unit. The similar method of HD is Cold deck imputation. K Nearest Neighbor Imputation (Knn) This method uses k nearest neighbor algorithms to estimate and replace missing data. It can estimate both qualitative attributes and quantitative attributes. K Means clustering method: Then KMI uses algorithm called nearest neighbour to impute the MVs in the same way as KNNI Fuzzy K Means clustering Imputation (FKMI) Unreferenced attributes for every uncompleted data are substituted by FKMI on the basis of membership degrees and cluster centroid values. Regression Imputation: Replace MVs with the values predicted from observed values Regression Equation: Y a0 a1 X Multiple Imputation: Multiple imputation (MI) illuminates the limitations of single imputation. It replaces each missing item with two or more acceptable values. 1.3 MISSING DATA MODEL BASED TECHNIQUES Maximum likelihood techniques are utilized to guess the parameters of a model defined for the all data. Maximum likelihood procedures that use variants of the ExpectationMaximization algorithm can deal with parameter estimation within the sight of missing data. MAXIMUM LIKELIHOOD: We can utilize this technique to get the variance covariance matrix for the variables in the model based on all the available data points, and after that obtained variancecovariance matrix to estimate our regression model [10] EXPECTATION MAXIMIZATION (EM) ALGORITHM: It depends on an expectation step and a maximization step, which are steady several times until maximum likelihood estimates are obtained. It requires a large sample length and that the data are missing at random (MAR) [4] and [2] Table 3: overview of model based me