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Off-Topic Discussion => General Discussion => Topic started by: Hudzy on October 20, 2002, 11:41:20 am

Title: Standard Deviation
Post by: Hudzy on October 20, 2002, 11:41:20 am

Ok, can anyone (maybe CP5670 :D) explain to me how standard deviation is worked out on a bunch of numbers like

76  83  52  75  90  85  88  79  86  74  73  85  79  86  81  77  84  72  79  84

for example?

Title: Standard Deviation
Post by: mikhael on October 20, 2002, 01:09:33 pm

The variance is a measure of how  spread out a distribution is. It is computed as the average squared deviation of each number from its mean.

First you get the mean of a population then you subtract the mean from each member of the population and square the results. You add this list together, and devide the result by the number of items in the list. The result is the variance of the series.  The standard deviation is the square root of the variance.

Title: Standard Deviation
Post by: Hudzy on October 20, 2002, 01:14:50 pm

Thanks. :D

Title: Standard Deviation
Post by: Hudzy on October 20, 2002, 01:32:11 pm

So am I correct in saying that the answer to the example would be 8.08?

Or am I just stupid? :nervous:

Title: Standard Deviation
Post by: mikhael on October 20, 2002, 02:37:39 pm

Quote

Originally posted by Hudzy
So am I correct in saying that the answer to the example would be 8.08?

Or am I just stupid? :nervous:

8.08332 by my calculations. This is biased though. I forgot to say that the unbiased estimate is given by dividing by "number of items minus one" (in this case, 19 rather than 20);

Title: Excuse me...
Post by: Star Dragon on October 20, 2002, 03:40:12 pm

But I don't see any points on those ears boy! :lol:

   We really should round these people up and make them work on stuff, like think tanks, or retooling industries for efficency and enviromental harmony...:yes: