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section6_handout_stat104_josh

# section6_handout_stat104_josh - Stat 104 Section 6 Josh...

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Stat 104 Section 6 Josh Zagorsky < [email protected] > Confidence Intervals 1. Recap: Truth Guess Confidence Interval μ ¯ X ¯ X ± z α/ 2 s n p ˆ p ˆ p ± z α/ 2 r ˆ p (1 - ˆ p ) n ρ r r ± z α/ 2 r 1 - r 2 n - 2 2. Comparing proportions in two different large samples ( n > 30), find the CI for the difference ˆ p 1 - ˆ p 2 : p 1 - ˆ p 2 ) ± z α/ 2 r ˆ p 1 (1 - ˆ p 1 ) n 1 + ˆ p 2 (1 - ˆ p 2 ) n 2 3. Comparing means in two different large samples ( n > 30), find the CI for the difference μ 1 - μ 2 : ( ¯ X - ¯ Y ) ± z α/ 2 s s 2 X n 1 + s 2 Y n 2 4. For small samples ( n < 30), use a t-statistic instead, but let Stata determine the degrees of freedom, since it’s kind of complicated. Stata Commands 1. Proportions prtesti n1 y1 n2 y2, count prtesti variable, by(control variable) 2. Means One dataset with control variable: ttest age, by(gender) unequal Different datasets: ttest cambridge==somerville, unpaired unequal If you only know sizes, means, and std devs for two samples: ttesti n1 m1 s1 n2 m2 s2, unequal 3. Matched Pairs

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section6_handout_stat104_josh - Stat 104 Section 6 Josh...

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