Stat 514 Fall 2010 Test 2 Take Home Questions

Bring these results and **
your calculations** to the exam on November 8. Keep answers on
separate sheets, as you will hand in the solution to one or more problems.

2. Calculate Pearson’s correlation, Spearman’s correlation, and Kendall’s tau to examine the relationship of calories and total fat in the candy bars. Create a plot of the data and test for association using each of the three measures.

3. A study was conducted to compare prices of boxes of candy bars at four internet candy stores. Here are the results (prices in dollars):

Store 1 | Store 2 | Store 3 | Store 4 | |

Milky Way | 28.95 | 28.80 | 36.00 | 23.79 |

Milky Way Midnight | 24.22 | 19.75 | 24.00 | 17.19 |

Three Musketeers | 32.32 | 29.80 | 37.00 | 22.32 |

Snickers | 37.95 | 38.40 | 48.00 | 36.82 |

Hershey's | 22.99 | 28.80 | 36.00 | 25.90 |

Based on these data, perform both a parametric and a nonparametric test of the null hypothesis that the price for candy bars is the same at the four stores.

4. The candy bar data include information about whether or not each candy bar contains transfat.

a. Perform a permutation test of homogeneity of row proportions, to see if the proportion of candy bars containing transfat differs between companies.

b. Is it appropriate to use the large sample chi-square approximation for the chi-square statistic for these data?

5. Describe a situation when analyzing two variables that the Pearson correlation would be a more appropriate measure of association than Kendall’s tau. Describe a situation when the reverse is true.