Standard Deviation

handloader1 · 12-09-2002, 09:47 PM

I have a equation for Standard Deviation; does anyone know if it is accurate? Standard Deviation = Bullet Diameter - Extream Spread Thanks in advance.

eldeguello · 12-10-2002, 07:17 AM

Standard deviation is a statistical expression of how much each observation in a series of values deviates from the norm of values in the series. In computing the standard deviation of a group of velocity measurements, the ONLY input data is each velocity measurement. The size of the bore or bullet, etc., has nothing to do with it. I have no idea what result the equation you have is suppposed to produce, but the way you describe it, it will NOT produce a standard deviation of velocities!!

Keep yore powder dry!!

handloader1 · 12-10-2002, 10:08 PM

eldeguello:

According to Sierra Technical help that is the equation to use.<img src=icon_smile_question.gif border=0 align=middle>

Briman · 12-10-2002, 10:45 PM

Here's a site that explains SD http://bmj.com/collections/statsbk/2.shtml

For a standard deviation of velocities, you need only the number of shots taken and the velocity of each shot.

<BLOCKQUOTE id=quote<font size=1 face='Verdana, Arial, Helvetica' id=quote>quote:<hr height=1 noshade id=quote>Standard Deviation = Bullet Diameter - Extream Spread <hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face='Verdana, Arial, Helvetica' size=2 id=quote>

If you use this equation which really isn't a logical equation at all, you will get a nonsensical answer.

Alcohol, Tobacco, and Firearms... who's bringing the chips?

eldeguello · 12-11-2002, 07:18 AM

I made the assumption that you were trying to determine the standard deviation of velocities for a series of shots, in which case bullet diameter is not a factor. As Briman has stated, if you use the formula that SIERRA GAVE YOU???, your answer would be nonsense!! However, perhaps you are trying to determine the standard deviation of some other measurement besides velocity. Even so, I believe using SIERRA'S??? formula, your answer is still not going to mean anything!!! What are you trying to determine the SD of, anyway??

Keep yore powder dry!!

handloader1 · 12-11-2002, 12:54 PM

Eldeguello:

I talked to Sierra today and the tech. gave me the wrong equation. He said there is alot more to figuring standard deviation than just an equation. He told me to let my chrony figure it out, but I want to know how to figure it out on paper. He is going to find out how to figure it out and E-mail me the process. Good luck.

Edited by - handloader1 on 12/11/2002 13:58:47

eldeguello · 12-12-2002, 07:14 AM

Handloader, I don't have my Lyman manuals right in front of me at this moment, but either No. 46 or No. 47 has a complete chapter on statistics for reloaders, and I am sure the derivation of standard deviation is covered in it!!

Keep yore powder dry!!

Deleted User · 12-12-2002, 12:36 PM

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Solitary Man · 12-12-2002, 01:28 PM

23 years ago when I was taking Stat class in college I could have told you all about standard deviation. I believe I made an "A" in that class as a matter of fact. Over the years, however, I've forgotten everything I ever knew about it and today I rely on my Shooting Chrony.

12-12-2002, 04:51 PM

The standard deviation is a measure of how widely values are dispersed from the average value (the mean).

So basically, if you have a collection of velocities, you find the mean of these values. Then you take an average value from the mean of the values on both sides. So if you say I have a std. dev. of velocities of 50fps, that doesn't mean your extreme spread is +/-50fps but you can count on your average spread to be that. It is called sigma in statistics.