Confidence intervals are an estimation of where a particular piece of data might fall into. For example, we can express proportions as percentages: instead of saying “9 out of 10 people agree” we might say 90% of people agree. If we aren’t sure about our data, we might have a confidence interval (between 8 and 10 people agree) instead of stating that 90% agree as an absolute fact. The TI-89 graphing calculator can easily calculate confidence intervals for you: you just need to read the results.
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A Statistical F-Test can be used to compare two variances, s1 and s2, by dividing them. The result is always a positive number (because variances are always positive).
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