To check pain-relieving medications for potential side effects on blood pressure, it is decided to give equal doses of each of four medications to test subjects. To control for the potential effect of weight, subjects are classified by weight groups. Subjects are approximately the same age and are in general good health. Two subjects in each category are chosen at random from a large group of male prison volunteers. Subjects' blood pressures 15 minutes after the dose are shown below. Research question: Is mean blood pressure affected by body weight and/or by medication type?

Systolic Blood Pressure of Subjects (mmHg)
Ratio of Subject's Weight to Normal Weight	Medication M1	Medication M2	Medication M3	Medication M4
Under 1.1	131	146	140	130
Under 1.1	135	136	132	125
1.1 to 1.3	136	138	134	131
1.1 to 1.3	145	145	147	133
1.3 to 1.5	145	149	146	139
1.3 to 1.5	152	157	151	141