USING R SOFTWARE

Problem 2.

Use the data contained in the file http://www.utdallas.edu/~ammann/stat3355scripts/Sleep.data

A description of this data is given in http://www.utdallas.edu/~ammann/stat3355scripts/Sleep.txt

The Species column should be used as row names.

a) Construct histograms of each variable and put them on the same graphics page.

b) The strong asymmetry for all variables except Sleep indicates that a log transformation is appropriate for those variables. Construct a new data frame that contains Sleep, replaces BodyWgt, BrainWgt, LifeSpan by their log-transformed values, and then construct histograms of each variable in this new data frame.

c) Plot LifeSpan vs BrainWgt with LifeSpan on the y-axis and include an informative title. Repeat but use the log-transformed variables instead. Superimpose lines corresponding to the respective means of the variables for each plot.

d) What proportion of species are within 2 s.d.'s of mean LifeSpan? What proportion are with 2 s.d.'s of mean BrainWgt? Answer these for the original variables and for the log-transformed variables.

e) Obtain and interpret the correlation between LifeSpan and BrainWgt. Repeat for log(LifeSpan) and log(BrainWgt).

f) Obtain the least squares regression line to predict LifeSpan based on BrainWgt. Repeat to predict log(LifeSpan) based on log(BrainWgt). Predict LifeSpan of Homo sapiens based on each of these regression lines. Which would you expect to have the best overall accuracy? Which prediction is closest to the actual LifeSpan of Homo sapiens?

Note: if X is the name of a data frame in R that contains two variables, say $x1, x2$ and you would like to create a new data frame with log-transformed values of the variables in X, then you can create a new object, named for example Xl, that is assigned the value X and then log-transform variables in this new data frame.

Kl = X names(X1) = paste("logx",1:2,sep="") X1$logx1 = log(X$x1) X1$logx2 = log(X$x2)