Thursday, June 8

Assignment 9.4 Task + RSG. In class notes on standard deviation

Note: The formula for standard deviation involves Sigma (Greek, "Sigma") or "sum" notation. x_i refers to the ith element in the data set, overline{x} is the mean x-value.

SD = sqrt{dfrac{sum_{i=1}^{N}(x_i - overline{x})^2}{N}}

Reading this formula means:

  1. Find the difference between each value and the mean

    (x_i - overline{x})

  2. Square those differences

    (x_i - overline{x})^2

  3. Find the sum of all of the squares

    sum_{i=1}^{N}(x_i - overline{x})^2

  4. Divide that value by N (the number of data elements in the set)

    dfrac{sum_{i=1}^{N}(x_i - overline{x})^2}{N}

  5. The Standard Deviation is the square root of the result

    SD = sqrt{dfrac{sum_{i=1}^{N}(x_i - overline{x})^2}{N}}

One way to understand the standard deviation is that it is kind of like the average distance from the mean in the data set.