How to Find t Critical Value on TI 83

Probability and Statistics > TI-83 for Statistics > how to find t critical value on ti 83

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IMPORTANT: The TI-83 doesn’t have a function to calculate the t critical value directly. In other words, you won’t find it listed on a menu as something like “invT”. However, you can calculate it; it just takes a couple of extra steps.

• if you want a t critical value for a two tailed test, follow the steps below. The confidence interval limits are the same as the t critical values.
• if you want the t critical value for a one tailed test, you can’t use the TI83 unless you program it (see this video for instructions ).

How to Find T Critical Value on TI 83: Steps

Sample Question: Calculate the two-talied t-critical value for 36 degrees of freedom (df = 36) for an alpha level of 0.05 (α = 0.05).

Step 1: Press the “STAT” key, then press the left arrow key to arrive at the Tests menu.

Step 2: Press “8” for TInterval.

Step 3: Arrow right to choose STATS. Press ENTER.

Step 3: Change the values in the list. For this sample question:

• Set the mean (Xbar) to 0
• Set Sx to the square root of your sample size. The sample size is df+1, so for this example press √37.
• Set n as your sample size. For this example, it’s 37.
• Set your confidence level, which is 1 – α For this example, set it to .95.

Step 4: Highlight CALCULATE and then press Enter. The t-critical value is The same as the given confidence level limits: 2.028.

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How to Find t Critical Value on TI 83 was last modified: October 31st, 2017 by

5 thoughts on “How to Find t Critical Value on TI 83”

1. Andale Post author

Echech,
I’ve double checked it and I don’t see an error. Can you be a little more specific about the problem you see with the critical value? Thanks.

2. sara

echech is right, this isn’t how to find a critical value. following these steps gives you the confidence interval (which you need the critical value to find)

3. Andale Post author

Hello, Sara,
The confidence limits are the same as the two tailed t critical value.
You do not need to know the critical value to find these limits — all you need are the alpha level and degrees of freedom.
Regards,
Stephanie

4. Anthony

Lets look at why this method does find the t critical value.
first the formula for confidence interval (x bar – error, x bar + error) or (x-E,x+E) for simpler notation.
E=t_(alpha/2)*(s/SquareRoot(n))
so if we let s=SquareRoot(n) E will be the t critical value for a two tail test.
E=t_(alpha/2)*(SquareRoot(n)/SquareRoot(n)) so the two square roots will cancel.
Now if x = 0, our confidence interval becomes (0-E,0+E) or just (-E,E)
putting it all together we get that the confidence interval is (-t_(alpha/2),t_(alpha/2))
Hence we can get the two tailed critical value using the confidence interval.
If you want a one tail critical value you must double the alpha value and take either the negative (left tail) or positive (right tail).

Hope this helps explain why this works!