![]() ![]() ![]() This tutorial explains how to calculate z-scores on a TI-84 calculator. The z-score of a given value is calculated as: z-score (x ) /. For a test using a 99% confidence level (e.g. A z-score tells us how many standard deviations away a given value is from the mean.For a test using a 95% confidence level (e.g.For a test using a 90% confidence level (e.g.The way to interpret this table is as follows: The following table displays the most common critical values for different values of α: We can also use a Critical Z Value Calculator to find z α/2 for some test.įor example, for some test that is using a 90% confidence level we can simply enter 0.1 as the significance level and the calculator will automatically return the value of 1.645 as the corresponding critical z value: And typically when we use z α/2 we take the absolute value. The corresponding z critical values on the outside of the table are -1.64 and -1.65.īy splitting the difference, we see that the z critical value would be -1.645. ![]() Step 4: Find the answer using a calculator: (1100 1026) / 209. Step 3: Write the standard deviation, into the z-score equation. Step 2: Put the mean,, into the z-score equation. Notice that the exact value of 0.05 doesn’t appear in the table, but it would be directly between the values. For this example question the X-value is your SAT score, 1100. To find the corresponding z critical value, we would simply look for 0.05 in a z table: Suppose we want to find z α/2 for some test that is using a 90% confidence level. Let’s jump in! How to find z α/2 using a z table Whenever you come across the term z α/2 in statistics, it is simply referring to the z critical value from the z table that corresponds to α/2. ![]()
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