| | Standard deviation - Wikipedia, the free encyclopedia |
 | | The standard deviation is defined as the square root of the variance. |
 | | A distinction is made between the standard deviation σ (sigma) of a whole population or of a random variable, and the standard deviation s of a subset-population sample. |
 | | When deciding whether measurements agree with a theoretical prediction, the standard deviation of those measurements is of crucial importance: if the mean of the measurements is too far away from the prediction (with the distance measured in standard deviations), then we consider the measurements as contradicting the prediction. |
| en.wikipedia.org /wiki/Standard_deviation (1436 words) |