'*********************************************************
'*      Program to demonstrate Chi-square Statistic      *
'* ----------------------------------------------------- *
'*    Reference: BASIC Scientific Subroutines, Vol. II   *
'*    By F.R. Ruckdeschel, BYTE/McGRAWW-HILL, 1981 [1].  *
'*                                                       *
'* ----------------------------------------------------- *
'* SAMPLE RUN:                                           *
'*                                                       *
'*  CHI-SQUARE CUMULATIVE DISTRIBUTION APPROXIMATION     *
'*                                                       *
'*   P(X)        X2       REAL X2                        *
'*  -----------------------------                        *
'*  0.05     124.5347     124.3                          *
'*  0.10     118.6326     118.5                          *
'*  0.15     114.5999                                    *
'*  0.20     111.4342                                    *
'*  0.25     108.7913     109.1                          *
'*  0.30     106.5055                                    *
'*  0.35     104.4821                                    *
'*  0.40     102.6610                                    *
'*  0.45     101.0018                                    *
'*  0.50      99.1944      99.3                          *
'*  0.55      97.6863                                    *
'*  0.60      96.0812                                    *
'*  0.65      94.3595                                    *
'*  0.70      92.4934                                    *
'*  0.75      90.4428      90.1                          *
'*  0.80      88.1446                                    *
'*  0.85      85.4893                                    *
'*  0.90      82.2522      82.4                          *
'*  0.95      77.7867      77.9                          *
'*  1.00       0.0000                                    *
'*  -----------------------------                        *
'*                                                       *
'*********************************************************
DEFINT I-N
DEFDBL A-H, O-Z
CLS
DIM x1$(25)
x1$(1) = "124.3": x1$(2) = "118.5"
x1$(5) = "109.1": x1$(10) = " 99.3"
x1$(15) = " 90.1": x1$(18) = " 82.4": x1$(19) = " 77.9"
PRINT "CHI-SQUARE CUMULATIVE DISTRIBUTION APPROXIMATION"
PRINT
PRINT " P(X)         Xý     REAL Xý "
PRINT " --------------------------- "
m = 100: i = 0
FOR y = .05 TO 1.01 STEP .05
  i = i + 1
  GOSUB 1000
  PRINT USING " #.##       ###.#     "; y; x; : PRINT x1$(i)
NEXT y
PRINT " --------------------------- "
END

'**************************************************
' Chi-square cumulative distribution approximation
' Good for m > 100.
' Reference: Statistics Manual, Crow, Maxfield and
' Davis (Dover, 1960).
' The input value is y, the probability, the output
' value is the corresponding Chi-square statistic.
'**************************************************
1000 x = y
  'Guard against zero discontinuity
  IF x <= 0 THEN x = EXP(-100)
  IF x > .5 THEN GOTO 1100
  x = -LOG(x)
  'Regressed table correction
  z = -.803 + 1.312 * x - .2118 * x * x + .016 * x * x * x
  GOTO 1200
1100 x = 1 - x
  'Guard against zero discontinuity
  IF x <= 0 THEN GOTO 1210
  x = -LOG(x)
  z = .803 - 1.312 * x + .2118 * x * x - .016 * x * x * x
1200 x = 2 / (9 * m)
  x = 1 - x + z * SQR(x)
1210 x = m * x * x * x
RETURN

'End of file Chisqa.bas