A researcher compares the effectiveness of two different instructional methods for teaching physiology. A sample of 181 students using Method 1 produces a testing average of 57.5. A sample of 227 students using Method 2 produces a testing average of 65. Assume the standard deviation is known to be 14.26 for Method 1 and 7.48 for Method 2. Determine the 98% confidence interval for the true difference between testing averages for students using Method 1 and students using Method 2. Step 1 of 2 : Find the critical value that should be used in constructing the confidence interval.