TI 83 Instructions - Confidence Intervals for mean (small samples) and one porportion

STATISTICS 2005

Fundamentals of Statistics Section 95

TI-83 Instructions - Confidence Intervals for the mean (small samples) and 1 proportion

Instructor: Pete Wildman

Fall Semester 1999

Confidence Intervals for t test and 1 sample proportions on the TI-83

Constructing confidence intervals for small normally distributed samples with unknown requires the use of the t-distribution. It is simple to do these problems on the TI-83

EXAMPLE 1: Suppose we randomly select 5 counties from New Jersey and measure their area. Suppose you get the following sample data:

221 329 476 103 362

Do the following

Enter this data into the one of your statistics editor lists

Hit STAT use the arrow keys to highlight TESTS

You should see the screen illustrated below:

Since the sample size is small (less than 30) and the population is known to normally distributed you should use a T Interval

Hit 8 for TInterval - here is the screen you should see:

Make sure Data is highlighted (use the arrow keys and enter to do this). Now enter the name of the list and the appropriate confidence level (In this case .90). When ready to calculate highlight the word calculate and hit enter. Did you get these answers?

EXAMPLE 2: The above example used data - this example uses only the summary statistics

Destructive testing: In many product quality tests you will deliberately destroy the product to find some information about it. If the product is expensive (such as cars or major appliances) you don't want to use a large sample size! Suppose you select a sample of 15 cars and subject them to crash tests and analyze your results for the dollar amount of damage done. If the mean dollar amount of damage is $15,789 with a standard deviation of $4782.50, find a 99% confidence interval for the mean

Do the following

Hit STAT and highlight TESTS. Do you have this screen?

Now hit 8 for Tinterval and this time highlight the word Stats. You should see the following screen:

Now enter the sample mean (In this case 15789), the sample standard deviation (4782.5) and the level of confidence (.99). Your screen should look as follows:

Now highlight Calculate and hit enter - did you receive these answers:

CONFIDENCE INTERVALS FOR PROPORTIONS OF ONE VARIABLE

The calculator makes the construction of the confidence interval for the population proportion very easy! Here is an example:

Suppose 500 students are randomly selected and asked if they own a personal computer. It is found that 135 of them own a personal computer. Find a 95% confidence interval for the true proportion of students who own personal computers

Do the following

Hit STAT and then highlight TESTS - you should have this screen

Select A for 1-PropZInt, you should see the following screen:

Now enter the data - for x the number of people who DID have computers (135) for n the sample size (500) and for C-Level: .95. After enter the data you should have this on the screen

Now highlight Calculate and hit enter - did you get these answers?