In a normal distribution, standard deviation measures how spread out the data is from the mean.
• 68% of data lies within 1 standard deviation (±1SD)
• 95% of data lies within 2 standard deviations (±2SD)
• 99.7% of data lies within 3 standard deviations (±3SD)
Example:
For Mean = 70 kg and Standard deviation (SD) = 8 kg
|
Deviation |
Formula |
Range (kg) |
|
±1SD (68%) |
Mean ± 1SD |
62 to 78 |
|
±2SD (95%) |
Mean ± 2SD |
54 to 86 |
|
±3SD (99.7%) |
Mean ± 3SD |
46 to 94 |