The following set of scores was obtained from a quiz: 4, 5, 8, 9, 11, 13, 15, 18, 18, 18, 20. The teacher computes the usual descriptive measures of central tendency and spread for these data and then discovers that an error was made. One of the 18s should have been a 16. Which of the following measures will NOT need to be changed from the original computations? (There may be more than one correct answer.)
A. Mean
B. Median
C. Standard deviation
D. IQR
E. They all will need to be changed.