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Calculating a standard deviation

26 July, 2019 - 10:10
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Example: The scores from 11 students on a quiz are 4, 7, 6, 3, 10, 7, 3, 7, 5, 5, and 9

  1. Order scores.
  2. Calculate the mean score.
  3. Calculate the deviations from the mean.
  4. Square the deviations from the mean.
  5. Calculate the mean of the squared deviations from the mean (i.e. sum the squared deviations from the mean then divide by the number of scores). This number is called the variance.
  6. Take the square root and you have calculated the standard deviation.
Table 12.3 Calculating a standard deviation

Score(Step 1, order)

Deviation from the mean

Squared deviation from the mean

 

3

3

9

 

3

3

9

 

4

2

4

(Step 4-5, complete the

calculations)

5

1

1

Formula:

5

1

1

media/image16.png

6

0

0

 

7

1

1

 

7

1

1

 

7

1

1

 

9

3

9

 

10

4

4

 

TOTAL = 66

 

52

 

(Step 2, calculate mean)

 

(Step 3, calculate deviations)

(Step 6, find the standard deviation)