What is the average site index of a stand if three plots have site indices of 70, 61, and 40?

What is the average site index of a stand if three plots have site indices of 70, 61, and 40?

• A. 60
• B. 70
• C. 61
• D. 65

Answer: (C)

When summarizing site productivity from several plots, using a representative central value is important, and the median often serves better than the mean when outliers are present. With site indices 70, 61, and 40, arranging them gives 40, 61, 70; the middle value is 61. This middle value reflects a typical condition for the stand without being skewed by the especially low plot or the high one. If you computed the mean, you’d get (70 + 61 + 40) / 3 = 57, which is pulled downward by the 40. So 61 is the best representative value in this context because it robustly summarizes the central tendency of the three plots. The other numbers correspond to the maximum or to a mean that’s affected by the outlier, not the typical site index for the stand.

When summarizing site productivity from several plots, using a representative central value is important, and the median often serves better than the mean when outliers are present. With site indices 70, 61, and 40, arranging them gives 40, 61, 70; the middle value is 61. This middle value reflects a typical condition for the stand without being skewed by the especially low plot or the high one. If you computed the mean, you’d get (70 + 61 + 40) / 3 = 57, which is pulled downward by the 40. So 61 is the best representative value in this context because it robustly summarizes the central tendency of the three plots. The other numbers correspond to the maximum or to a mean that’s affected by the outlier, not the typical site index for the stand.