C**********************************************************************
C    THIS SUBROUTINE GIVES TABLED VALUES FOR THE T DISTRIBUTION UP
C    TO 100 DEGREES OF FREEDOM AND THEN DOES A CRUDE INTERPOLATION.
C**********************************************************************
      FUNCTION TVALUE (IDF)
C***********************************************************************
C     DECLARATIONS
C***********************************************************************
      REAL T(100)
C***********************************************************************
C     DATA STATEMENTS
C***********************************************************************
      DATA T /12.706,4.303,3.182,2.776,2.571,2.447,2.365,2.306,2.262,2.2
     1 28,2.201,2.179,2.160,2.145,2.131,2.120,2.110,2.101,2.093,2.086,2.
     2 080,2.074,2.069,2.064,2.060,2.056,2.052,2.048,2.045,2.042,2.040,2
     3 .037,2.035,2.032,2.030,2.028,2.026,2.024,2.022,2.021,2.020,2.018,
     4 2.017,2.015,2.014,2.013,2.012,2.010,2.009,2.008,2.007,2.006,2.005
     5 ,2.004,2.004,2.003,2.002,2.001,2.000,2.00,1.999,1.998,1.997,1.997
     6 ,1.996,1.996,1.995,1.995,1.995,1.994,1.994,1.993,1.993,1.992,1.99
     7 2,1.991,1.991,1.990,1.990,1.989,1.989,1.988,1.988,1.988,1.987,1.9
     8 87,1.987,1.986,1.986,1.986,1.986,1.986,1.985,1.985,1.984,1.984,1.
     9 984,1.983,1.983,1.982/
      IF (IDF.GT.100) GO TO 10
      TVALUE=T(IDF)
      RETURN
   10 TV=1.982-(FLOAT(IDF)-100.)*.008
      IF (TV.LT.1.96) TV=1.96
      TVALUE=TV
      RETURN
      END