Reference Standard Deviation
The Reference Std Dev is the standard deviation you expect from the standard samples. For a good estimate of the standard deviation you should use at least 25 groups of observations. Calculate a range for each group then average them. You can convert the resulting average range to an estimate of standard deviation using the following table:
|
a |
an |
a |
an |
|
2 |
0.8862 |
10 |
0.3249 |
|
3 |
0.5908 |
11 |
0.3152 |
|
4 |
0.4857 |
12 |
0.3069 |
|
5 |
0.4299 |
13 |
0.2998 |
|
6 |
0.3846 |
14 |
0.2935 |
|
7 |
0.3698 |
15 |
0.2880 |
|
8 |
0.3512 |
16 |
0.2831 |
|
9 |
0.3367 |
17 |
0.2787 |
Multiply the average range of a set of samples, each of size a (taken from the table), by the corresponding value for an. For example: if you calculated an average range of 0.45 using the mean ranges of a set of samples, where each group contained four samples, the standard deviation estimate would be: s = 0.4857 x 0.45 = 0.2186.
If you don't make an entry for Reference Std Dev, the program will calculate it in the same way as for the Reference mean. The same considerations apply.