the Children's Depression Inventory (CDI), developed from Beck's Depression Inventory is a self-report instrument with 27 sets of statements. Higher scores indicate higher levels of depression. Scores above 13 are said to indicate a Major Depressive Disorder (MDD) and few false positives have been reported. A random sample of 20 fifth grade students was selected and given the test. Their scores were as follows: 9, 10, 11, 9, 8, 9, 17, 2, 7, 11, 6, 12, 9, 10, 9, 9, 8, 10, 14, 1. What is the standard deviation for the group