The general form for a confidence interval is:

Sample Statistic z^*. SE

where -z^* &z^* are the values on aStandard Normal Distribution, N(0,1) that the Confidence Level % lies between. An example for a 95% confidence interval can be seen in the picture below. Here we can see the-z^*&z^*on the horizontal axis, -1.960 and 1.960. Consider how this relates back to our 95% rule that says approximately 95% of the normal distribution is between 2 standard deviations either side of the mean.

123123z

0.025

-1.96

0.025

1.96

What are the z and zvalues for an 80% confidence interval

1.645

2.054

1.44

2.327

1.282