Technically, the standard deviation is defined as the square root of the variance. But where the standard deviation comes in handy is when it is used to describe part of a distribution. Standard deviations give us an idea of how much data is contained within a certain area of a distribution curve. This information is especially useful when using normal distribution curves (which you’ll, no doubt, learn about during your statistics course).
Sample problem: Find the standard deviation for the heights of the top 12 buildings in London, England. The heights, (in feet) are: 800, 720, 655, 655, 625, 600, 590, 529, 513, 502, 502, 502.
Step 1: Enter the above data into a list. Press the STAT button and then press ENTER. Enter the first number (800), and then press ENTER. Continue entering numbers, pressing ENTER after each entry.
Step 2: Press STAT.
Step 3: Press the right arrow button (the arrow keys are located at the top right of the keypad) to select Calc.
Step 4: PressENTER to highlight 1-Var Stats.
Step 5: Press ENTER again to bring up a list of stats. The standard deviation (Sx) for the above list of data is 96.57 feet (rounded to 2 decimal places).