96 Introduction to Robust Estimation and Hypothesis Testing 3.12.6 R Function idealf The R function idealf(x), written for this book, computes the ideal fourths for the data stored in the R variable x. 3.13 Some Outlier Detection Methods This section summarizes some outlier detection methods, two of which are variations of so-called boxplot techniques. One of these methods has, in essence, already been described, but it is convenient to include it here along with a description of relevant software. 3.13.1 Rules Based on Means and Variances We begin with a method for detecting outliers that is known to be unsatisfactory, but it is a natural strategy to consider, so its limitations should be made explicit. The rule is to declare X i an outlier if