Computing for Research I Spring 2012 Exploratory Data Analysis and Hypothesis Testing February 21...
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Transcript of Computing for Research I Spring 2012 Exploratory Data Analysis and Hypothesis Testing February 21...
Computing for Research ISpring 2012
Exploratory Data Analysis and Hypothesis TestingFebruary 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?• Confidence intervals– for continuous variables– for categorical variables
Immediate command for CIs
Continuous:cii N xbar s
Binary:cii N phatorcii N x
Confidence intervals
• For a continuous variable:mean varlist
• Example:* estimate means of ceramide variablesmean c18ceramidemean totalc - s1pc1
Additional options
tab initialre initialmean c18ceramide, over(initialre)
mean c18ceramide, vce(bootstr)
mean c18ceramide, vce(bootstr) over(initialre)mean c18ceramide, over(initialre)
mean c18ceramide, level(90)
Confidence intervals for proportion
proportion varlist
Examplesproportion failure
proportion failure death initialre
proportion failure, vce(bootstr)proportion failure, cluster(patient)proportion failure, level(90)
Hypothesis Testing
• A number of different approaches• Options– nonparametric vs. parametric– continuous vs. categorical (vs. other?)– one vs. two vs. more than two groups
One sample t-tests
• ttesti N mean sd null • ttest varname == null• ttest var1 == var2 *paired
• Examples:ttesti 20 48 2.75 50 ttest c18c == 10ttest frombaselines1p==100ttest frombaselinec18==100
Two sample t-teststtesti N1 mean1 sd1 N2 mean2 sd2ttest varname1 == varname2, unpairedttest varname, by(groupvar)
Examples:
ttest c18, by(sex)ttest c18, by(sex) unequal
Nonparametric?
• ranksum: two group comparison• kwallis: >= two group comparison
• signrank: matched pairs signed ranks test• signtest: sign test of matched pairs
Nonparametric?*nonparametric testsranksum c18, by(sex)kwallis c18, by(sex)
use ceramide.alldata, clearkeep if cycle==3gen c18dif = frombaselinec18-100signrank c18dif=0signrank frombaselinec18=100signtest c18dif=0signtest frombaselinec18=100
Anova
• anova y x(note that x is assumed to be categorical)anova y x1 x2
Examples:anova c18c initialre
One sample binomial tests
• prtest and bitest• Difference? – prtest uses large sample approximations– bitest uses exact test
bitest varname==p0bitesti N x p0
One sample binomial testsuse "SCBC2004.v9.dta", clearreplace ercat=. if ercat==9gen ercatn=cond(ercat==2,0,1)replace ercatn=. if ercat==.tab ercat ercatn
bitest ercatn=0.50bitest ercatn=0.65prtest ercatn=0.65
Two (or more) sample binomial tests
tab y x, exacttab y x, chi
tab ercatn gradetab ercatn stage