 |
| Standard Deviation for continuous series |
|
| In this series too deviations may be taken either from the actual mean or from standard mean. The calculations will be simplified if the deviation are taken from assumed mean. |
| |
| Step 1: |
| |
| Take the midpoint of different classes. |
| |
| Step 2: |
| |
| Subtract assumed mean from each midpoint to obtain (m-a). |
| |
| Step 3: |
| |
If the width of the class interval is same, then divide each (m-a) by c,  |
| |
| Step 4: |
| |
| Multiply each frequency with corresponding deviation i.e., fd and obtain Sfd. |
| |
| Step 5: |
| |
 |
| |
| Step 6: |
| |
| Apply the formula |
| |
 |
| |
 |
| |
| Example: |
| |
| Calculate the variance and standard deviation from the following data. |
| |
 |
| |
| Suggested answer: |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
