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Confidence Intervals for Two Proportions

Example:
Part way through the 1996 baseball season, the Texas Rangers had played 37 games at home and 27 games away. They won 27 of the home games and 13 away. Find their winning proportions at home and away. Find a 90% confidence interval for the difference between these proportions.

Solution:
Since you have 2 proportions and trying to find out the confidence interval, you can use 2-prop Z interval. From the statistical data list, press "F4" (INTR), then press "F1" (Z), and then press "F4" (2-P).

Enter the confidence level, sample 1, sample 1 size, sample 2, sample 2 size. Then press "F1" (CALC) to calculate. Notice that the proportions are already calculated and appear under the interval.

The winning proportion at home is about 0.730. The proportion for away games is about 0.481. The 90% confidence interval is about (0.05, 0.45).