       Student's T Confidence Interval [StudentTCI]

• To: mathgroup at smc.vnet.net
• Subject: [mg111347] Student's T Confidence Interval [StudentTCI]
• From: davef <davidfrick2003 at yahoo.com>
• Date: Wed, 28 Jul 2010 02:55:13 -0400 (EDT)

```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?

```

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