Decrease visibility.
diff --git a/src/main/java/org/apache/commons/math4/stat/descriptive/rank/Percentile.java b/src/main/java/org/apache/commons/math4/stat/descriptive/rank/Percentile.java
index 9bd7e62..ca71269 100644
--- a/src/main/java/org/apache/commons/math4/stat/descriptive/rank/Percentile.java
+++ b/src/main/java/org/apache/commons/math4/stat/descriptive/rank/Percentile.java
@@ -564,7 +564,7 @@
      * @return work array sliced from values in the range [begin,begin+length)
      * @throws MathIllegalArgumentException if values or indices are invalid
      */
-    protected double[] getWorkArray(final double[] values, final int begin, final int length) {
+    private double[] getWorkArray(final double[] values, final int begin, final int length) {
         final double[] work;
         if (values == getDataRef()) {
             work = getDataRef();