Table of Contents
The process of calculating confidence intervals on a TI-84 calculator involves using specific statistical functions and formulas to determine a range of values that is likely to contain the true population mean or proportion with a certain level of confidence. This can be done by inputting relevant data and selecting the appropriate function on the calculator. The resulting confidence interval can then be interpreted to make accurate inferences about the population.
Calculate Confidence Intervals on a TI-84 Calculator
A confidence interval (C.I.) is a range of values that is likely to include a with a certain degree of confidence.
This tutorial explains how to calculate the following confidence intervals on a TI-84 calculator:
- Confidence interval for a population mean; σ known
- Confidence interval for a population mean; σ unknown
- Confidence interval for a population proportion
Example 1: C.I. for a population mean; σ known
Find a 95% confidence interval for a population mean, given the following information:
- sample mean x = 14
- sample size n = 35
- population standard deviation = 4
Step 1: Choose Z Interval.
Press Stat and then scroll over to TESTS. Highlight 7:ZInterval and press Enter.
Step 2: Fill in the necessary information.
The calculator will ask for the following information:
- Inpt: Choose whether you are working with raw data (Data) or summary statistics (Stats). In this case, we will highlight Stats and press ENTER.
- σ: The population standard deviation. We will type 4 and press ENTER.
- x: The sample mean. We will type 14 and press ENTER.
- n: The sample size. We will type 35 and press ENTER.
- C-level:The confidence level We will type 0.95 and press ENTER.
Lastly, highlight Calculate and press ENTER.
Step 3: Interpret the results.
Once you press ENTER, the 95% confidence interval for the population mean will be displayed:
Example 2: C.I. for a population mean; σ unknown
Find a 95% confidence interval for a population mean, given the following information:
- sample mean x = 12
- sample size n = 19
- sample standard deviation = 6.3
Step 1: Choose T Interval.
Press Stat and then scroll over to TESTS. Highlight 8:TInterval and press Enter.
Step 2: Fill in the necessary information.
The calculator will ask for the following information:
- Inpt: Choose whether you are working with raw data (Data) or summary statistics (Stats). In this case, we will highlight Stats and press ENTER.
- x: The sample mean. We will type 12 and press ENTER.
- Sx: The sample standard deviation. We will type 6.3 and press ENTER.
- n: The sample size. We will type 19 and press ENTER.
- C-level:The confidence level We will type 0.95 and press ENTER.
Lastly, highlight Calculate and press ENTER.
Step 3: Interpret the results.
Once you press ENTER, the 95% confidence interval for the population mean will be displayed:
The 95% confidence interval for the population mean is (8.9635, 15.037).
Example 3: C.I. for a population proportion
Find a 95% confidence interval for a population proportion, given the following information:
- number of “successes” (x) = 12
- number of trials (n) = 19
Step 1: Choose 1 Proportion Z Interval.
Press Stat and then scroll over to TESTS. Highlight 1-PropZInt and press Enter.
Step 2: Fill in the necessary information.
The calculator will ask for the following information:
- x: The number of successes. We will type 12 and press ENTER.
- n: The number of trials. We will type 19 and press ENTER.
- C-level:The confidence level We will type 0.95 and press ENTER.
Lastly, highlight Calculate and press ENTER.
Step 3: Interpret the results.
Once you press ENTER, the 95% confidence interval for the population proportion will be displayed:
The 95% confidence interval for the population proportion is (0.41468, 0.84848).