Re: Student's T Confidence Interval [StudentTCI]

*To*: mathgroup at smc.vnet.net*Subject*: [mg111351] Re: Student's T Confidence Interval [StudentTCI]*From*: Ray Koopman <koopman at sfu.ca>*Date*: Wed, 28 Jul 2010 07:25:16 -0400 (EDT)*References*: <i2ok8k$827$1@smc.vnet.net>

On Jul 27, 11:55 pm, davef <davidfrick2... at yahoo.com> wrote: > I don't understqnd how this function is working. > > I have a sampe mean of 12, standard deviation of 21, sample size of 10 > and level of significance of .05. > > The t critical value I get from a table for a 2-tail test (p=. > 05/2=0.025 and df=10-1=9) is 2.262 > > My standard error of the estimate is std dev divided by square root of > n = 21/(10)^1/2 = 0.0664. > > So my confidence interval should be 12 +/- 2.262(0.0664) = -3.0215 to > 27.0215 > > But in Mathematica this...: > > \[Mu] = 12 > \[Sigma] = 21 > df = 10 - 1 > StudentTCI[\[Mu], \[Sigma] , df, ConfidenceLevel -> .975] > > ...gives me this... > > {-44.3852, 68.3852} > > ...and this... > StudentTCI[\[Mu], \[Sigma] , df, ConfidenceLevel -> .95] > > ...gives me this... > > {-35.5053, 59.5053} > > What don't I undersatnd about how to use the StudentTCI function? StudentTCI[ 12, 21/Sqrt[10], 9, ConfidenceLevel->.95 ] {-3.0225,27.0225}