🔒 Locked

standard deviation

Started by davidko Oct 10, 2001 at 10:27 PM 6 replies 1.6k views

Original Post

Oct 10, 2001 at 10:27 PM

My statistics really sux, so here''s my question. To calculate standard deviation for a set of points, you take the mean, find the variance, and square root it, etc. etc. But...how would you find the standard deviation for each individual point? I believe it is a measure of uncertainty for each point, but I didn''t think you could do that. An algorithm (linear regression) calls for these values, but I wasn''t sure how to calculate it...oh how I wish I had a statistics book somewhere lying about. Thanks for any help...

Null and Void

163

Null and Void

Oct 10, 2001 at 10:35 PM

The standard deviation of a single point is its ZScore. This is how you get it:


          (point - mean)
ZScore = ----------------
         (std. deviation)

[Resist Windows XP''s Invasive Production Activation Technology!]

davidko

Author

davidko

Oct 10, 2001 at 10:49 PM

ahhh...

ZScore. I have absolutely no recollection of that word from stats. musta been sleeping or something. thanks!

DDnewbie

Oct 16, 2001 at 3:47 PM

Hi,

I don't quite understand what is meant by standard deviation of ONE point!??

Isn't standard deviation a measure of how a collection of points is spread around the mean? That is, a "spreadingmeasure".

You can of course calc the standard deviation of one stochastic variable, but that's a function and not a point.

/Mankind gave birth to God.

Edited by - silvren on October 16, 2001 4:48:28 PM

Zipster

511

Zipster

Oct 16, 2001 at 11:57 PM

The same thing happens when working with derivatives... how can you find the slope of the line tangeant to the function at a point when we need two points to define a line? We can of course do this, but it will always be off by an infinitely small amount. I don''t recall anything about ZScore either, so I can''t directly tell you how it applies in that sense, but it''s somewhat related!

Null and Void

163

Null and Void

Oct 17, 2001 at 12:07 AM

ZScore is the number of ''standard deviations'' away a point is from the mean. It''s a pretty simple concept.

[Resist Windows XP''s Invasive Production Activation Technology!]

Beer Hunter

122

Beer Hunter

Oct 17, 2001 at 1:10 AM

Zipster - yes, it will be off by an infinitely small amount. Keyphrase: "infinitely small".

DDnewbie

Oct 18, 2001 at 2:05 PM

OK,

Thanks! the concept is somewhat clearer to me now.
I think I''ll read up on that stuff.

cheers

/Mankind gave birth to God.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.