My Math Forum none in +/- 2 standard deviations

 Algebra Pre-Algebra and Basic Algebra Math Forum

April 8th, 2013, 02:50 PM   #1
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none in +/- 2 standard deviations

I have for sample:
Quote:
 50.98 48.8 65.18 69.64 28.22 102.74 72.59 114.56 81.96 66.2 95.08 120.58 71.98 36.69
Although it's small and I'm inexperienced, I'm wondering why there's nothing outside (+/-) 2 standard deviations (2?), which is 55.34 (? = 27.67) on the mean (?) 73.23 ; the range is < 17.89, > 128.57.

I think ? would be smaller so there is something in that range (+/-2?). Or perhaps there's some concept I don't understand which would make it possible for the whole sample to be limited in 1?.

 April 9th, 2013, 12:01 PM #2 Global Moderator   Joined: May 2007 Posts: 6,770 Thanks: 700 Re: none in +/- 2 standard deviations 2? is the bound for approximately 95% of a sample. Since your sample size is 14, it is not surprising that they are all inside this range.
 April 9th, 2013, 02:39 PM #3 Member   Joined: Jan 2012 From: Montreal, Canada Posts: 30 Thanks: 0 Re: none in +/- 2 standard deviations Thanks. At least I know it's not erroneous but it's weird for me to understand. Well I guess it's hard to have 1/20 in the range when there's not even 20 items. I didn't think about it that way.
April 9th, 2013, 02:43 PM   #4
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Re: none in +/- 2 standard deviations

Darn! I can't edit my last post. Well this is its PS.

Quote:
 Originally Posted by DynV Or perhaps there's some concept I don't understand which would make it possible for the whole sample to be limited in 1?.
I don't know if I was confused thinking the samples was limited in 1? or I was confused writing it, thinking of 2?.

Anyway I'm not concerned about the issue anymore.

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