MATH 251, Probability and Statistics I, Fall 2005, Fri. Nov. 18, Day 37 hit reloadAfter class, example now works

Reading:  Start 7.2, thru p. 497.   Read the rest, lightly, in self-defense (no HW required on it)
Hand in: 

Sec. 7.2, two-sample, by hand.  A table is a good way to organize the work, see example
 For problems involving calculating a CI and/or a test, give the Difference and  SEDiff as well as the answers asked for. 
7.83 iron deficiency  (FYI, most US pediatricians recommend iron supplements for both...)
7.82 cocaine & birthweight
7.68&69 Bread Read them and Do only this:  7.69a.  Tell what analysis you would do for 7.69. 
7.66 flat screens  Read a, remember how to do it. Do b, c. 
    +7.67 new screens now
7.59 what's wrong?
7.60, 61 short answer questions
7.57 soft drink size--missing information  (A frustrating thing about published info--like this, they often leave out what you need to check up on them, investigate further.)

 Read, 
discuss
 
 

 

 Optional
(more practice)
SPSS handout for 7.1, t procedures
Exam 2 Due today by 1pm under my door or in my hand.
Quiz back.
<>What is the significance to Statistics of the Guinness Stout Bottle ?
~~~~~~~~~~~~~~~

Sec. 7.2, Comparing two means"Two-sample tests". Notes Day 36
Summary:  Two SRS's, independent, from distinct  populations. (Populations are normally distributed) Robust? Yes...but...p. 493

We use the Difference of the two x-bars,  diff =  xbar1 - xbar2 = .
 The Standard Error of the difference  xbar1 - xbar2 :
 substitute sample standard deviations for population standard deviations, and our z's are replaced by t's.
<>For testing, if Ho is "population means are equal"
"Two-sample t-statistic" <>
For doing by hand:  df = smaller of (n1- 1) and (n2- 1).  Will give a "conservative" result.
From a computer:  df = complicated formula on p. 498.  Produces non-integer degrees of freedom.  Very good if both sample sizes are at least 5. Unsuitable for doing by hand.
CI for µ1 - µ2, difference of means,  is 

--SPSS will do our computations when we are given raw data. Next.

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