CONFIDENCE INTERVALS

Confidence Intervals are used to help find a population parameter when the population is too large to perform a census on all members of the population.  Confidence intervals are performed at a certain level of confidence, and tell how likely it is that the sample that was drawn from the population will contain the true population parameter.  The most common parameters that are performed are population means and population proportions.  When you hear someone saying that a certain poll was conducted and the results were 62% with a margin of error of +/- 3%, that is an example of a confidence interval.

What is a Confidence Interval?

Z-interval for the Mean

The z-interval for the mean is the confidence interval that is used when you know the population standard deviation.  Out of the two intervals for the mean, this one is used less frequently, because the population standard deviation is not generally known.  Videos show how to do hand calculation, and how to use the TI-84 and TI-Nspire graphing calculators to help generate the confidence intervals.

Z-Interval for the Mean
Z-Interval for the Mean-TI-84 - Given Stats
Z-Interval for the Mean-TI-84 - Given Data
Z-Interval for the Mean-TI-Nspire - Given Stats
Z-Interval for the Mean-TI-Nspire-Given Data
Minimum Sample Size for Confidence Intervals of Means

t-Interval for the Mean

The t-interval for the mean is the confidence interval that is used when you know the sample standard deviation.  Out of the two intervals for the mean, this one is used more frequently, because the population standard deviation is not generally known.  Videos show how to do hand calculation, and how to use the TI-84 and TI-Nspire graphing calculators to help generate the confidence intervals.

t-Interval for the Mean
t-Interval for the Mean TI-84-Given Data
t-Interval for the Mean TI-84-Given Stats
t-Interval for the Mean-TI-Nspire-Given Data
t-Interval for the Mean-TI-Nspire-Given Stats

1-Proportion Z-interval

A one proportion z-interval is used when we are trying to get an estimate for the proportion or percentage of the population that agree or disagree with a certain topic.  This is the formula that is used to report polling information, and is how they compute the margin of error.  We have all heard new stations say something along the lines "57% of the population agree with the new bill with a margin of error of +-3%..."  Now you can learn how they calculate those values.

1-Proportion z-Interval
Minimum Sample Size for a 1-Proportion z-Interval