Using TI-83 to Find Confidence Interval: Overview
Confidence intervals give you a range of values which is likely to include an unknown parameter for the population. A simple example: you are going in for surgery at a local hospital. The surgeon tells you your expected hospital stay is “about a week.” In reality, patients who have undergone the same procedure stay in the hospital a minimum of five days and a maximum of ten. That’s your confidence interval: five days to ten days. A confidence level is something slightly different: it’s how sure you are of your confidence interval. You’re probably 99% sure that your stay will be five to ten days, but anything could happen, right? You could make a miraculous recovery, or you could be one of the rare people that get a post-op infection. Either way, you can’t be 100% confident. So you say your 99% confidence interval is five to ten days.
Using TI-83 to Find Confidence Interval: Steps
Sample problem: For x = 20, and n = 24, construct a 98% confidence interval for p, the true population proportion.
Step 1: Press STAT.
Step 2: Right arrow over to “TESTS.”
Step 3: Arrow down to “A:1–PropZInt…” and then press ENTER.
Step 4: Enter your x-value: 2 0.
Step 5: Arrow down and then enter your n value: 2 4.
Step 6: Arrow down to “C-Level” and enter . 9 8.
Step 7: Arrow down to calculate and press ENTER. The calculator will return the range (.65636, 1.0103).
Tip: Instead of arrowing down to select A:1–PropZInt…, press Alpha and MATH instead.
That’s you using TI-83 to find confidence interval in easy steps!
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