NAEP Science Grade 12

Category - Earth Science

Hydrologists are helping establish the variability of discharge on a particular river. They determine the average discharge of the river over the past 100 years using historical data. Which of the following is the best measure of the variability of this data set? 
  1. The median
  2. The standard deviation
  3. The mode
  4. The arithmetic mean
Explanation
Correct Response: B. Standard deviation is a measure of the variability of a data set. It is the square root of the variance of the data set, where the variance represents how spread out a data set is from the mean. In this way standard deviation is useful for determining the variability of a river's discharge over a period of time. The median (A) measures the middle value of a data set not its variability, while the mode (C) is the most common value in the data set, and the arithmetic mean (D) is the average of the data set, a value that the hydrologists have already calculated and that does not measure variability.
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