TI83/84: DIY Inverse chi-square program

The inverse chi square function isn’t pre-loaded on TI-83 and TI-84 calculators. Inverse chi square returns a critical value we use in hypothesis tests and confidence intervals for population variance.
Here is a simple 3-line program for inverse chi square you can enter in your calculator.
If you find this video helpful, give it a thumbs up.
Go to PRGM, NEW, 1. Create New
At the Name = prompt, the cursor is already in alpha mode, type a short name. I used INVCHI.
ENTER
And we’re ready to write the program!
: Input “AREA RIGHT:”,A
: Input “DF:”,D
: Disp solve(1-X2cdf(0,X,D)-A,X,0)
:
Click 2nd MODE to exit the program.
Now go to PGRM, EXEC, and you’ll see your INVCHI program in the list. Click to select it.
prgmINVCHI is pasted to the home screen. Click ENTER to activate it.
You should see the AREA RIGHT prompt.
Test it with the following (press ENTER after each entry):
AREA RIGHT: .05
DF: 13
It may take a few seconds to find the solution. Check answer: 22.362
Press ENTER again to find another chi square critical value.
Reload the program any time in PRGM, EXEC.
Tips for building and using the program:
- The colon adds itself to the start of each line automatically.
- If you need to exit out of a menu while programming, use 2nd MODE.
- Your work saves automatically. Go back to PRGM, EDIT, INVCHI to continue working.
- Input and Disp commands are in PRGM, I/O. Solve (or Solver) is in MATH. X2cdf is in 2nd VARS.
- For AREA RIGHT, always enter area to the right of chi square.

[@brandonmancilla3402]

As much as I shouldn't, I absolutely despise looking at the table for the value I need. I really appreciate the video! Thank you!

[@maxedoutvibes]

For some reason this wasn't an included lesson in my stats class, very glad I was able to find it here.

[@KevinPalmer-p9u]

Your voice was very relaxing, 10/10 would recommend to a friend

[@Splunchy]

Thank you very much. This has been very handy and I appreciate explaining all the steps.

[@raiddear8063]

Thank you so much !!! You explained it so easily !!

[@Poke_Leaf]

Thank you so much for this! Needed this function for a stats course!

[@quantquill]

Glad it helped!

[@K4RM0_SENSEI]

thank you so much !!!

[@scottcampbell7596]

This helps me so much. Thank you!!

[@stm3265]

This is so helpful thank you!

[@joseboy1993]

I love you! lol thanks so much!

[@AerstalRiley]

Vielen Dank

[@saulblackfire]

You save me! Thanks!

[@Mothballzz]

thank you ! It worked on my physical calculator ti-84 plus, so it doesn't just work for computer software

[@jakemamula8067]

dope as hell

[@GabbiBelleS]

pretty awesome! thanks for sharing.

[@ElektraBoom]

THANK YOU!!!

[@chizhang3263]

thanks very helpful

[@jimiwild564]

Thank you!

[@quantquill]

You're welcome!

[@Mayzaf14]

Thank you so much!

[@maxpercer7119]

pretty slow program, but useful

[@quantquill]

Hi, Max, thanks for the comment. If you find a way to speed it up, I'm all ears! It seems to be an inbuilt feature of the calculator that it takes a while to crunch through the computations.

[@tagumanicholas6572]

'I followed the steps and when I hit enter after putting the df I get "Err:Syntax 1: Quit 2:Goto

[@quantquill]

Hi Taguma, if you have a Ti 83 or TI 84 that looks like the calculator simulator, then we know the program works. So you should double check your code is set up correctly -- every space, comma and period matters. If you have any other calculator, like a TI 84 CE, then the code or the steps may be a little different. This program only applies to this specific calculator.

[@tonyt.641]

can you run this for the left side as well or no?

[@quantquill]

Yes, if you put the area to the right of your left-tailed X2 value. In the example in the video, I got a right-tailed X2 by indicating it had 5% (0.05) of area to the right. If you want the X2 that has 5% of area to the left, then it will have 95% of area to the right, so you'd put 0.95 in as "Area Right". Hope that helps!

[@tonyt.641]

@@quantquill thank you!

[@rosienazario3254]

Is there a way to do Area Left?

[@quantquill]

Hi Rosie, since 100% of area is under the curve, the chi square critical value with (for example) 5% of area to the left is the same as the one with 95% of area to the right. So if you are asked for a left tailed chi square, you can run the program and put "1 - area to the left" in your Area Right field. Hope that helps!