               STUDENT'S T DISTRIBUTION CRITICAL VALUES

Michael Lloyd (http://www.hsu.edu/faculty/lloydm/ti/prgmtabl.html)
Henderson State University

DESCRIPTION
Given the area under the Student's t probability density function,
the critical value(s) are found.

INSTRUCTIONS

1. Select the form of area you wish to enter, or quit the program. The
TAIL selections 1 and 2 are often used for hypothesis testing, selections
3 and 4 correspond to t tables found in statistics and probability books,
and selection 5 is often used for confidence intervals.
  1. 1 TAIL TEST - area is from the critical value to infinity.
  2. 2-TAIL TEST - area is the sum of the left and right tail areas. 
    Because the t pdf is symmetric, only the positive critical value
    will be displayed.
  3. AREA 0 -> t - area is from 0 to a positive critical t value.
  4. AREA -OO -> t - area is from negative infinity to a a critical t
    value.
  5. CONF. INTERVAL - area is in the middle and what is left over is
     split between the tails. Because the t pdf is symmetric, only the 
    positive critical value will be displayed.
2. Enter the area. SIG stands for the signicance level alpha of the 
hypothesis   test; CONF LEVEL stands for confidence level c.
3. Enter the degrees of freedom.
4. The critical value will be displayed.

VERSION HISTORY
1.0 - December 1996 - original version called X2VAL
1.1 - April 1997
1.2 - October 1997
1.3 - Jan 2006 - Renamed to INVX2 to make consistent with TI-89 
  statistical APP function
1.4 - March 2007 - added copyright
1.5 - August 2015 - updated file to .8xp

VARIABLES USED
C = areas
K = degrees of freedom, number of points
prgmZZMENU menu for critical values
T = critical t value

PROGRAM LISTING

Disp "VERSION 1.4","(C)2007 M LLOYD"
"STUDENT'S t DIST"\->\Str1
"t"\->\Str2
prgmZZMENU
Input "DEG. FREEDOM=",K
K+1\->\K
TInterval 0,\root\(K),K,2C
upper\->\T
Disp "t=",T
DelVar Str1
