Multivariate Data Visualization

Multivariate analysis deals with the statistical analysis of observations where there are multiple responses for each observational unit. Let X be an n μ p data matrix where the rows represent observations and the columns, variables. We will denote the variables by X1, X2, ..., Xp. In most cases it is necessary to sphere the data by subtracting out the means and dividing by the standard deviations. If outliers are a possibility then a robust sphering method such as that discussed by Venables and Ripley (1997, p.266) should be tried too. Important special cases are p = 1, 2, 3 which correspond to univariate, bivariate and trivariate data.