Managing diabetes People with diabetes measure their fasting plasma glucose (FPG; measured in units of milligrams per milliliter) after fasting for at least 8 hours. Another measurement, made at regular medical checkups, is called HbA. This is roughly the percent of red blood cells that have a glucose molecule attached. It measures average exposure to glucose over a period of several months. The table below gives data on both HbA and FPG for 18 diabetics five months after they had completed a diabetes education class.27 STEP4 Subject HbA

(%)

FPG

(mg/mL)

1 6.1 141 2 6.3 158 3 6.4 112 4 6.8 153 5 7.0 134 6 7.1 95 7 7.5 96 8 7.7 78 9 7.9 148 Subject HbA

(%)

FPG

(mg/mL)

10 8.7 172 11 9.4 200 12 10.4 271 13 10.6 103 14 10.7 172 15 10.7 359 16 11.2 145 17 13.7 147 18 19.3 255

(a) Make a scatterplot with HbA as the explanatory variable.
Describe what you see.

(b) Subject 18 is an outlier in the x direction. What effect do you think this subject has on the correlation? What effect do you think this subject has on the equation of the least-squares regression line? Calculate the correlation and equation of the least-squares regression line with and without this subject to confirm your answer.

(c) Subject 15 is an outlier in the y direction. What effect do you think this subject has on the correlation? What effect do you think this subject has on the equation of the least-squares regression line? Calculate the correlation and equation of the least-squares regression line with and without this subject to confirm your answer.