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Computing for Research I Spring 2012

Computing for Research I Spring 2012. Exploratory Data Analysis and Hypothesis Testing February 21 Primary Instructor: Elizabeth Garrett- MAyer. Exploratory Data Analysis. We’ve already discussed some basic stuff sum and sum, detail tab What other sorts of exploration might we do?

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Computing for Research I Spring 2012

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  1. Computing for Research ISpring 2012 Exploratory Data Analysis and Hypothesis Testing February 21 Primary Instructor: Elizabeth Garrett-MAyer

  2. Exploratory Data Analysis • We’ve already discussed some basic stuff • sum and sum, detail • tab • What other sorts of exploration might we do? • Confidence intervals • for continuous variables • for categorical variables

  3. Immediate command for CIs Continuous: cii N xbar s Binary: cii N phat or cii N x

  4. Confidence intervals • For a continuous variable: mean varlist • Example: * estimate means of ceramide variables mean c18ceramide mean totalc- s1pc1

  5. Additional options tab initialre initial mean c18ceramide, over(initialre) mean c18ceramide, vce(bootstr) mean c18ceramide, vce(bootstr) over(initialre) mean c18ceramide, over(initialre) mean c18ceramide, level(90)

  6. Confidence intervals for proportion proportion varlist Examples proportion failure proportion failure death initialre proportion failure, vce(bootstr) proportion failure, cluster(patient) proportion failure, level(90)

  7. Hypothesis Testing • A number of different approaches • Options • nonparametric vs. parametric • continuous vs. categorical (vs. other?) • one vs. two vs. more than two groups

  8. One sample t-tests • ttestiN mean sd null • ttestvarname == null • ttest var1 == var2 *paired • Examples: ttesti 20 48 2.75 50 ttest c18c == 10 ttest frombaselines1p==100 ttest frombaselinec18==100

  9. Two sample t-tests ttesti N1 mean1 sd1 N2 mean2 sd2 ttestvarname1 == varname2, unpaired ttestvarname, by(groupvar) Examples: ttest c18, by(sex) ttest c18, by(sex) unequal

  10. Nonparametric? • ranksum: two group comparison • kwallis: >= two group comparison • signrank: matched pairs signed ranks test • signtest: sign test of matched pairs

  11. Nonparametric? *nonparametric tests ranksum c18, by(sex) kwallis c18, by(sex) use ceramide.alldata, clear keep if cycle==3 gen c18dif = frombaselinec18-100 signrank c18dif=0 signrank frombaselinec18=100 signtest c18dif=0 signtest frombaselinec18=100

  12. Anova • anova y x (note that x is assumed to be categorical) anovay x1 x2 Examples: anova c18c initialre

  13. One sample binomial tests • prtest and bitest • Difference? • prtest uses large sample approximations • bitest uses exact test bitestvarname==p0 bitesti N x p0

  14. One sample binomial tests use "SCBC2004.v9.dta", clear replace ercat=. if ercat==9 gen ercatn=cond(ercat==2,0,1) replace ercatn=. if ercat==. tab ercatercatn bitestercatn=0.50 bitestercatn=0.65 prtestercatn=0.65

  15. Two (or more) sample binomial tests tab y x, exact tab y x, chi tab ercatn grade tab ercatn stage

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