Main Index > TI 83 > Using TI-83 to Find Confidence Interval

## 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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Does the TI-83 have a special function to calculate population proportion confidence intervals for small populations?

David,

Can you post your question on our forum? Click the “forums” tab at the top. One of our mods will be happy to help :)

Stephanie

How do you do this without the calculator?

Hope this helps: Find a confidence interval for a proportion