5.X4 

A study was conducted to determine whether automobile repair charges are higher for female customers than for male customers. Twenty auto repair shops were randomly selected from the telephone book. Two cars of the same age, brand, and engine problem were used in the study. For each repair shop the two cars were randomly assigned to a man and woman participant. 

  file <- "http://www.uvm.edu/~rsingle/stat211/data/extra/ch5_6-22.txt"
  dat<-read.table(file, header=T, na.strings=c("NA",".")) 

a) Are repair costs higher for female customers than for male customers? Use a T-test at the .05 level to answer the question. State the statistic, d.f., p-value and a conclusion.

b) Clearly state each of the assumptions for a valid test *and* whether or not they are met for this data.

c) Answer the question in part (a) using the appropriate non-parametric test. State the statistic, p-value and a conclusion.

d) Why are the results similar/different for part (a) and (c)? Based on your answer to part (b), which test is better to use in this case?