Percentage Points of the Chi-Squared Distribution

ASA091 is a C library which computes the percentage points of the Chi-Squared probability distribution, by Best and Roberts.

ASA091 is Applied Statistics Algorithm 91. Source code for many Applied Statistics Algorithms is available through STATLIB.


The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.


ASA091 is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:


NORMAL, a C library which samples the normal distribution.

PROB, a C library which evaluates and inverts many probability distibutions.

TEST_VALUES, a C library which contains sample values for a number of distributions.

UNIFORM, a C library which samples the uniform distribution.


Original FORTRAN77 version by Donald Best and DE Roberts; C version by John Burkardt.


  1. Donald Best, DE Roberts,
    Algorithm AS 91: The Percentage Points of the Chi-Squared Distribution,
    Applied Statistics,
    Volume 24, Number 3, 1975, pages 385-390.
  2. William Cody, Kenneth Hillstrom,
    Chebyshev Approximations for the Natural Logarithm of the Gamma Function,
    Mathematics of Computation,
    Volume 21, Number 98, April 1967, pages 198-203.
  3. John Hart, Ward Cheney, Charles Lawson, Hans Maehly, Charles Mesztenyi, John Rice, Henry Thacher, Christoph Witzgall,
    Computer Approximations,
    Wiley, 1968,
    LC: QA297.C64.
  4. BL Shea,
    Algorithm AS 239: Chi-squared and Incomplete Gamma Integral,
    Applied Statistics,
    Volume 37, Number 3, 1988, pages 466-473.
  5. Michael Wichura,
    Algorithm AS 241: The Percentage Points of the Normal Distribution,
    Applied Statistics,
    Volume 37, Number 3, 1988, pages 477-484.

Source Code:

Last revised on 08 November 2018.