6.1 Five micrograms of a drug were injected into rats minutes after their blood pressures had been taken. After 30 minutes, their blood pressures were retaken. The data for the six animals are as follows: Rat Number Control Pressure Drug Pressure 120 110 135 113 116 96 aUAWNE 110 104 145 132 116 85 (a) Is there evidence at the 5% level of significance that the drug alters the blood pressure? (b) Construct a 95% confidence interval for the mean difference. 208 COMPARISON OF TWO GROUPS: t-TESTS AND RANK TESTS (c) Construct a 99% confidence interval for the mean difference. (d) Why is the 99% interval wider than the 95% interval