Data Learn — Mean, Median and Spread Basics | datalearn.site
Six core measures — mean, median, mode, range, variance and standard deviation — each with its formula, its unit and a worked example on the set 1, 2, 3, 4, 5, 6, 8, 9.
The mean is the sum divided by n. On the set 1, 2, 3, 4, 5, 6, 8, 9 the sum is 38 and n is 8, giving 4.75. Its unit is the same as the data, because you never leave the original scale.
The median with n = 8 is the mean of the two middle values: (4 + 5) / 2 = 4.5. It is simultaneously the 2nd quartile, the 5th decile and the 50th percentile of the set. Its unit is also the unit of the data.
The mode is the most frequent value. The worked set contains no repeats, so it has no mode — record this as 'none' rather than forcing a number.
On narrow screens, swipe or scroll the plate sideways.
The range is maximum minus minimum: 9 − 1 = 8, in the original units. It is the quickest spread figure and the most sensitive to a single extreme value.
The variance averages the squared distances from the mean and is therefore reported in squared units. The standard deviation takes the square root, returning to the original units, which is why it is the spread figure most often quoted alongside a mean.
Kurtosis and skewness round out a full summary: skewness measures asymmetry, kurtosis measures tail heaviness. Both are dimensionless ratios.
Further reading