| PERCENT STD |
Notes
on Percent Standard Deviation
Standard deviation is an incomplete representation
of measured data behavior and it can be misleading to those who are not familiar
with statistics. Therefore to obtain a meaningful number you have to
combine Standard Deviation with the Average Value.
Here is an example of a typical problem: let us
assume that you fired two strings with 5 shots each at different velocity
ranges. In the example below all values are in feet/sec and all results are
rounded off to 2 and 4 decimal points.
|
Shot |
String-1 |
String-2 |
|
1 |
1010.00 |
110.00 |
|
2 |
1015.00 |
115.00 |
|
3 |
1020.00 |
120.00 |
|
4 |
1025.00 |
125.00 |
|
5 |
1030.00 |
130.00 |
|
|
|
|
|
Average Value |
1020.00 |
120.00 |
|
Standards Deviation |
7.9056 |
7.9056 |
|
Percent Standard Deviation |
0.7750 |
6.5880 |
If you relied on Standard Deviation alone, you would be in error by a factor of 8.5, which is a significant amount. Error factor calculation (6.588/0.775)=8.5.
String-1 and String-2 have the same Standard Deviation, yet you know that the shots in String-2 are 8.5 times worse. In order to solve this problem we have provided Percent Standard Deviation, which performs all the work for you and is defined as follows;
| (Standard
Deviation) |
X 100 |
This is a far superior
performance indicator of your shots. For those who are used to Standard
Deviation, we still provide it for the compatibility.