To find the standard deviation, follow these steps:
- Calculate the mean (average) of the data set by adding all the numbers and dividing by the number of data points.
- Calculate the deviation of each data point from the mean by subtracting the mean from each value.
- Square each deviation to get positive values.
- Find the sum of these squared deviations.
- For a sample, divide this sum by (n - 1), where n is the number of data points; for a population, divide by n. This gives the variance.
- Take the square root of the variance. This result is the standard deviation.
This process measures how spread out the data points are around the mean, with a higher standard deviation indicating greater variability. For example, with data points 46, 69, 32, 60, 52, 41:
- Mean = 50
- Deviations: -4, 19, -18, 10, 2, -9
- Squared deviations: 16, 361, 324, 100, 4, 81
- Sum of squares = 886
- Variance = 886 / (6 - 1) = 177.2
- Standard deviation = √177.2 ≈ 13.31
This method applies whether the data is a full population or a sample (adjusting the divisor accordingly).