1 Computing Confidence Intervals using the TI-83 The TI-83 can compute an ENTIRE confidence interval from either summary statistics or data. These functions can be accesed by pressing STAT  TEST

2 Estimating  from a Large Sample If n > 30 the sample is considered to be large, regardless of its distribution’s shape. Press STAT, choose TESTS and choose 7:ZInterval

3 Example A study of 50 iris flowers revealed a mean petal length of 2.03 cm, sample standard deviation of 0.27 cm. Compute a 90% confidence interval for the population mean petal length. x-bar = 2.03, s = 0.27, n = 50 are our summary statistics. Since n>30 okay to use Zinterval as well as s in place of  Step 1: Press STAT, selects TESTS, select Zinterval Step 2: For method of input (Inpt:) select STATS, since we have summary statistics. Step 3: Enter 0.27 for , 2.03 for x-bar and 50 for n. Step 4.Set C-Level( Confidence Level) to.90 Step 5: Select Calculate. (Double Check Entries First)

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5 Estimating  from a Small Sample If n ≤ 30 the sample is considered to be small, the population must be normal and  unknown. Press STAT, choose TESTS and choose 8:TInterval

6 Example Consumer Reports gave the following information about the life(hours) of AA batteries in toys. Assume the population is normally distributed, compute a 95% confidence interval to estimate the true mean life of AA batteries in toys

7 Example Since n = 16 which is less than 30,  is unknown and the population is normal we use a TInterval. Since we have data we must enter it into a list. Step 1: Press STAT, choose Edit, enter the values into L1. Step 2: Press STAT, select TESTS, select 8:Tinterval. Step 3: Select Data for method Input. Step 4: Enter L1 for List, 1 for Freq Step 5.Set C-Level( Confidence Level) to.95 Step 6: Select Calculate. (Double Check Entries First)

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9 Estimating p If the sample is a SRS, binomial and np  5 and nq  5 are both satisfied. Press STAT, choose TESTS and choose A:1-PropZInt ˆˆ

10 Example Example: In a survey of 2503 men and women aged 18 to 75 years and representative of the nation as a whole, 1927 people said the homeless are not adequately assisted by the government. Find a point estimate and a 90% confidence interval for the proportion p of adults in the general population who agree that the homeless are not adequately assisted by the government. n = 2503, x = 1927, since we have more than 5 success and 5 failures it is okay to use a 1-PropZInt. Step 1: Press STAT, select TESTS, select A:1-PropZInt. Step 2: Enter the number of success for x and sample size for n. Step 3.Set C-Level( Confidence Level) to.90 Step 4: Select Calculate. (Double Check Entries First

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