lect21v1_1up

lect21v1_1up - Stat 104 Quantitative Methods for Economists...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Stat 104: Quantitative Methods for Economists Class 21: Confidence Intervals- Two Samples 1 Midterm Exam: October 18 s 7pm at night-locations to be announced s Open book/Open notes s Topics Include b Mean and Variance of Data, Correlation, Covariance, Regression b Basic probability, 2x2 tables, conditional, indep. b Random Variables, means, variance, sums b Binomial and Normal Distributions b CI for means and proportions (all 95%) 2 Confidence Interval for the Confidence Coefficient s Recall that if we have two random variables X and Y, a measure of association is given by the correlation coefficient defined by ρ = Corr X Y ( , ) s Using data, we may obtain an estimate of ρ which we call r. A 95% confidence interval is given by 3 r r n ±-- 196 1 2 2 . Example: Haircut and TV Watching s What is the correlation between how much one spends on a haircut and the hours of tv they watch in a week ? s From class data, Correlation of haircut and tv = -0.182 4 2 2 1 1 ( .182) 1.96 .182 1.96 2 80 2 ( .4,.036) r r n-- - ± = - ±-- = - Interpretation of the Confidence Interval ? Summary so Far μ α X X z s n ± /2 Truth Truth Guess Guess Confidence Interval Confidence Interval 5 ρ α α p p p z p p n r r z r n ±- ±-- / / ɵ ɵ ɵ ( ɵ ) 2 2 2 1 1 2 The Confidence Interval Recipe s By now, you should realize that all confidence intervals have the same form: point timate confidence efficien standard deviation f point e imate F G I J ± F G I J * F G I J s Remember this formula. It says how to create a confidence interval for everything we will be doing. All you need is a point estimate and a measure of how variable the estimate is (and this info usually comes from the CLT). 6 estimate coefficient of point estimate H K H K H K Comparison of Two Proportions s Very often we are interested in comparing two proportions: b The difference in unemployment rates between Republicans and Democrats b The difference in percentage if households that plan to buy a car during the next year in northeastern states versus southeastern states. 7 Two Sample Test s We have two independent samples from populations of interest....
View Full Document

This note was uploaded on 03/27/2012 for the course STATS 104 taught by Professor Michaelparzen during the Fall '11 term at Harvard.

Page1 / 39

lect21v1_1up - Stat 104 Quantitative Methods for Economists...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online