Finding critical values and reading a z-table are an essential part of statistics. Critical values are used in hypothesis testing, and can help you use the standard normal distribution graph to make predictions about data. The TI-89 Titanium graphing calculator makes light work of finding critical values, because of its built in z-table. The TI-89 Titanium’s Stats/List Editor contains a simple menu where you can look up a critical value for a left-tailed tests in seconds.
Sample problem: find α = .012 for a left-tailed test on a standard normal distribution.
Step 1: Press Apps, scroll to the Stats/List Editor, and press Enter.
Step 2: Press F5 2 1, to get to the Inverse Normal screen.
Step 3: Enter .012 in the Area box.
Step 4: Enter 0 for the mean, μ and 1 for the standard deviation, σ.
Step 5: Press Enter.
Step 6: Read the result: the calculator should state “Inverse = -2.25713“. This is your critical value.
Tip: If you are given a mean and standard deviation, enter them in place of 0 and 1 in Step 4.
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