Title: Are Values Missing Randomly in Survey Research
Abstract: Many missing data studies have simulated data, randomly deleted values, and investigated which method of handling the missing values would most closely approximate the original data. Regression procedures have emerged as the most recommended methods. If the values are missing randomly, these procedures are effective. If, however, the values are not missing randomly, the use of regression procedures to impute values for missing data is questionable. The purpose of this study was to determine if values were missing randomly in samples selected from the student cohort of the National Education Longitudinal Study of 1988. Four samples were selected: two samples of eight variables, average intercorrelation of.2 and .4 respectively; and two samples offour variables, average inter-correlation of.2 and .4 respectively. All cases containing more than one missing value were selected. The pattern of simultaneously missing values for each selected case was determined. If values were missing randomly, it was assumed the proportion of jointly missing values would be equivalent. Chi square goodness offit analysis indicates the missing values are not missing randomly (p Different methods of handling missing values may produce different results. When Jackson (1968) entered data on all the available variables in a discriminant analysis, the significance of the regression coefficients (as well as the interpretation of the importance) of individual variables changed with the missing value method used. Witty and Kaiser (1991) reported that the regression coefficients and total variance accounted for by the variables changed depending on the method used to handle missing values. After reanalyzing three studies of private/public school achievement, Ward Jr. and Clark III (1991) concluded that the method used to handle missing data influenced the outcome of these studies. They further add that the iterative regression procedures are considered the most effective. Witty (1993), however, found the regression procedures to be less effective in replicating the population covariance matrix and mean vector than listwise and pairwise deletion when sample sizes were large (2000) and no more effective when sample sizes were small (200). She attributed this to lack of randomness in the missing data. The dilemma is further entangled when ignoring the missing data problem may lead to analysis of data that is of dubious value. Publication of the results of this analysis without correctly handling the missing values may jeopardize the credibility of the organization conducting the survey and preparing the analysis and report:... (Little & Smith,1983, p. S 18). Researchers are thus faced with the task of determining which missing data method is most appropriate for their research. Unfortunately, there is no established correct method for handling missing values when the mechanism causing them is unknown. This study examines the mechanism causing the missing values by investigating the pattern of missing values. The purpose of this study was to determine if simultaneously missing values were missing randomly from four samples selected from the National Education Longitudinal Study of 1988 (NELS-88). Because the NELS-88 data base is readily accessible and widely used, information concerning the pattern of missing values and its influence on missing data procedures is needed. Literature Review Methods that are currently being used to handle missing values include deletion methods (listwise and pairwise deletion) and imputation methods (mean substitution and various regression procedures). The most common solution to the missing data problem is probably listwise deletion. This procedure is the default option in several computer programs (LISREL, SPSS, NCSS). This method discards cases with a missing value on any variable and thus is very wasteful of data. If the data are assumed to be missing completely at random, this procedure is acceptable. …
Publication Year: 1994
Publication Date: 1994-11-01
Language: en
Type: article
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Cited By Count: 3
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