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4. Z-INT: p1− p2.: Confidence interval for the difference of two
proportions, p
1
-p
2
, for large samples with unknown population
variances.
5. T-INT: 1 µ.: Single sample confidence interval for the population mean,
µ, for small samples with unknown population variance.
6. T-INT: µ1−µ2.: Confidence interval for the difference of the population
means, µ
1
- µ
2
, for small samples with unknown population variances.
Example 1 – Determine the centered confidence interval for the mean of a
population if a sample of 60 elements indicate that the mean value of the
sample is ⎯x = 23.3, and its standard deviation is s = 5.2. Use
α = 0.05. The confidence level is C = 1-α = 0.95.
Select case 1 from the menu shown above by pressing @@@OK@@@. Enter the
values required in the input form as shown:
Press @HELP to obtain a screen explaining the meaning of the confidence
interval in terms of random numbers generated by a calculator. To scroll
down the resulting screen use the down-arrow key
˜. Press @@@OK@@@ when
done with the help screen. This will return you to the screen shown above.
To calculate the confidence interval, press @@@OK@@@. The result shown in the
calculator is:
Press @GRAPH to see a graphical display of the confidence interval
information:
SG49A.book Page 8 Friday, September 16, 2005 1:31 PM