Structure

 

  1. Find the mean (In this example it is 1+2+3+4+5/5 = 3)
  2. Find the total amount of data (In this example there are 5 as there are 5 given modes of transport, therefore N = 5)
  3. To complete the top half of the fraction, , add an extra column to the table. For each piece of data subtract the given value from the mean ( in this example) and square the result

i.e. car = 2 people, so (2 – mean(3)) 2 = 4

 

  1. Add up the total of all the results from step 3 (The sum of) This result can now replace the top half of the fraction ( in this example, it’s 4+1+0+1+4=10)
  2. To find the bottom half of the fraction, like the equation says to do so subtract 1 from the total amount of data in the dataset, 5-1 = 4
  3. The fraction should look like this now:
  4. Pop all the calculation into the calculator

e.g.

How do you get to school? Total
Bus 1 (1-3) = 4
Car 2 (2-3) = 1
Bike 3 (3-3) = 0
Walk 4 (4-3)= 1
Helicopter 5 (5-3) = 4
Total 15 10

n = 5-1 = 4

S = 1.58