Treatment of Multivariate Outliers in Incomplete Business Survey Data
The distribution of multivariate quantitative survey data usually is not normal. Skewed and semi continuous distributions occur often. In addition, missing values and non response is common. All together this mix of problems makes multivariate outlier detection difficult. Examples of surveys where these problems occur are most business surveys and some household surveys like the Survey for the Statistics of Income and Living Condition (SILC) of the European Union. Several methods for multivariate outlier detection are collected in the R package modi. This paper gives an overview of modi and its functions for outlier detection and corresponding imputation. The use of the methods is explained with a business survey dataset. The discussion covers pre and post processing to deal with skewness and zero inflation, advantages and disadvantages of the methods and the choice of the parameters.