MSM 709

Hand-in Assignment # 3: 50 points

Due Tuesday, April 26^th

Please answer all questions in complete sentences and type up your responses. All graphs and computations are to be generated in Minitab. Minitab graphs can be cut and pasted into Word documents (select Edit >Copy Graph, then have Word open in another window and just hit Paste.) Finally, please staple any multiple pages together.

Open the Minitab file Cholest.MTW. Recall that, to open this file, click on File, then Open Worksheet and then click on the button that says “look in Minitab sample data folder.”

This data set consists of the blood cholesterol levels of 28 heart attack victims 2, 4 and 14 days following the attack. The levels of 30 individuals who had not had an attack were taken as a control. Note that where there is an asterisk in a column, this simply means the measurement was not available. Minitab will ignore these empty cells.

1. Construct boxplots for all four data sets and display them on the same graph for comparison.

2. Which of the data sets has the highest median? Is this surprising? Why or why not?

3. Since the first three columns of data come from the same patients, it would be appropriate to investigate correlation among any two of them. Does there appear to be a linear relationship between a patient’s blood cholesterol 2 days after a heart attack and 4 days later? How about between 2 days and 14 days later? Construct appropriate scatter plots, describe each scatter plot as we did in class (positive or negative relationship? Strong or weak? Etc.) and find and interpret the correlation coefficient in each case.

4. Find the equation of the least squares regression line for the 4-day data as a function of the 2-day data (that is, the 4-day data is the response variable or y-coordinate and the 2-day data is the predictor or x-coordinate)

5. Use the regression equation found in part d. to predict the blood cholesterol of a patient 4 days after a heart attack who has a 2-day level of 250.