**Confidence
Interval for the Population Proportion **

**Brief Instructions**

Press
*STAT*, choose *TESTS*, choose *1-PropZInt...*
and press *ENTER*. Enter the correct numbers
next to the corresponding symbols. *C-Level*
is short for *Confidence Level*. Choose *Calculate*
and press *ENTER*. The confidence
interval appears below *1-PropZInt* in
the correct format. You may have to round the endpoints to a reasonable number
of decimal places.

**Detailed Instructions**

To demonstrate this procedure, suppose we have 34 successes in 80 trials and want 98% confidence in our result.

Press
*STAT*, choose *TESTS* and then choose *1-PropZInt...*
and press *ENTER*. You will see the *1-PropZint* input screen.

Enter
the correct numbers next to the corresponding symbols. To enter a number, move
the cursor to the right of the symbol using the arrow buttons and enter the
number in the usual fashion. *C-Level* is short for *Confidence Level*.

When you have finished, the numbers should appear as shown below.

_{}

If your
numbers are in the correct position, put the cursor on *Calculate* and press *ENTER*.
You should see the following display.

_{}

Since the number of successes and the number of trials have at most 2 significant digits, the confidence interval should have three-place accuracy. So in this case, the confidence interval is approximately (0.296, 0.554).