Hypothesis Test and Confidence Interval for comparing 2 independent means

• First, go to Stat, Basic Statistics, 2 sample t .
• The following screen will appear.

• Click on "Samples in Different Columns".
• Enter the two different groups that you want to compare into First and Second.
• Determine if you can assume equal variances.
• If the ratio of the standard deviations(the largest standard deviation on top) is over 2, do not check the box for Assume equal variances.
• If the ratio of the standard deviations (the largest standard deviation on top) is less than 2, check the box for assuming equal variances.
• Click on Options. The following box will appear.

• To Compute a Hypothesis Test
• Fill in the test mean in the box. Most likely this number will be equal to zero.
• Chose the alternative that matches your alternative hypothesis.
• To Compute a Confidence Interval or Bound.
• Enter your level of confidence.
• Do not worry about the blank for test mean
• Next pick the alternative that matches your alternative hypothesis.
• If you want a two sided test,  select "not equal" as your alternative.
• If you want a one sided test, , select "less than"  or  "greater than".

Note: Your screen may look a little different; however, you should have the same boxes to fill in for Confidence and Alternative.

Two-Sample T-Test and CI: Normal, High

Two-sample T for Normal vs High

         N      Mean     StDev   SE Mean
Normal  15     47.89      3.93       1.0
High    15     90.12      1.96      0.51

Difference = mu Normal - mu High
Estimate for difference:  -42.23
95% CI for difference: (-44.60, -39.87)
T-Test of difference = 0 (vs not =): T-Value = -37.26  P-Value = 0.000  DF = 20