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# 1.9 - Summary of important R code

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The main components of R code used in this chapter follow with components to modify in red, remembering that any R packages mentioned need to be installed and loaded for this code to have a chance of working:

• summary(DATASETNAME)
• ◦ Provides numerical summaries of all variables in the data set.
• t.test(Y~X,data=DATASETNAME,conf.level=0.95)
• ◦ Provides two-sample t-test test statistic, df, p-value, and 95% confidence interval.
• 2*pt(abs(Tobs),df=DF,lower.tail=F)
• ◦ Finds the two-sided test p-value for an observed 2-sample t-test statistic of Tobs.
• hist(DATASETNAME\$Y)
• ◦ Makes a histogram of a variable named Y from the data set of interest.
• boxplot(Y~X,data=DATASETNAME)
• ◦ Makes a boxplot of a variable named Y for groups in X from the data set.
• beanplot(Y~X,data=DATASETNAME)
• ◦ Makes a beanplot of a variable named Y for groups in X from the data set.
• ◦ Requires the beanplot package is loaded.
• mean(Y~X,data=DATASETNAME); sd(Y~X,data=DATASETNAME)
• ◦ Provides the mean and sd of responses of Y for each group described in X.
• favstats(Y~X,data=DATASETNAME)
• ◦ Provides numerical summaries of Y by groups described in X.
• Tobs <- t.test(Y~X,data=DATASETNAME,var.equal=T)\$statistic; Tobs

B<-1000

Tstar<-matrix(NA,nrow=B)

for (b in (1:B)){

Tstar[b]<-t.test(Y~shuffle(X),data=DATASETNAME,var.equal=T)\$statistic

}

• ◦ Code to run a for loop to generate 1000 permuted versions of the test statistic using the shuffle function and keep track of the results in Tstar.
• pdata(abs(Tobs),Tstar,lower.tail=F)
• ◦ Finds the proportion of the permuted test statistics in Tstar that are less than -|Tobs| or greater than |Tobs|,
• Tobs <- compareMeans(Y~X,data= DATASETNAME); Tobs

B<-1000

Tstar<-matrix(NA,nrow=B)

for (b in (1:B)){

Tstar[b]<-compareMeans(Y~X,data=resample(DATASETNAME))

}

• ◦ Code to run a for loop to generate 1000 bootstrapped versions of the data set using the resample function and keep track of the results of the statistic in Tstar.
• qdata(c(0.025,0.975),Tstar)
• ◦ Provides the values that delineate the middle 95% of the results in the bootstrap distribution (Tstar).