What is Pearson's first coefficient of skewness formula?

• A. (Mean − Median) / SD
• B. (Mode − Mean) / SD
• C. (Mean − Mode) / SD
• D. (Mean − Mode) / Variance

Answer: (C)

This formula tests how the average value sits relative to the most frequent value, scaled by how spread out the data are. It’s calculated as the mean minus the mode, divided by the standard deviation. The sign of the result tells which way the distribution leans: if the mean is larger than the mode, you get a positive skew (tail to the right); if the mean is smaller than the mode, you get a negative skew (tail to the left). Using the standard deviation in the denominator keeps the measure unitless and comparable across different data sets.

The choice that uses mean minus median would describe a related idea, but it’s a different form of skewness. Using variance in the denominator would change the scale and isn’t the standard version.