fisher.test {ctest} | R Documentation |
fisher.test
performs Fisher's exact test for testing the null
of independence of rows and columns in a contingency table with
fixed marginals.
fisher.test(x, y, alternative = "two.sided", workspace = 200000, hybrid = FALSE)
x |
either a two-dimensional contingency table in matrix form, or a factor object. |
y |
a factor object; ignored if x is a matrix. |
alternative |
indicates the alternative hypothesis and must be
one of "two.sided" , "greater" or "less" .
You can specify just the initial letter. Only used in the 2 by
2 case. |
workspace |
an integer specifying the size of the workspace used in the network algorithm. |
hybrid |
a logical indicating whether the exact probabilities (default) or a hybrid approximation thereof should be computed. In the hybrid case, asymptotic chi-square probabilies are only used provided that the ``Cochran'' conditions are satisfied. |
If x
is a matrix, it is taken as a two-dimensional
contingency table, and hence its entries should be nonnegative
integers. Otherwise, both x
and y
must be vectors of
the same length. Incomplete cases are removed, the vectors are
coerced into factor objects, and the contingency table is computed
from these.
In the one-sided 2 by 2 cases, p-values are obtained directly using the hypergeometric distribution. Otherwise, computations are based on a C version of the FORTRAN subroutine FEXACT which implements the network developed by Mehta and Patel (1986) and improved by Clarkson, Fan & Joe (1993). The FORTRAN code can be obtained from http://www.netlib.org/toms/643.
"htest"
containing the following
components:
p.value |
the p-value of the test. |
alternative |
a character string describing the alternative hypothesis. |
method |
the string "Fisher's Exact Test for Count Data" . |
data.name |
a character string giving the names of the data. |
Cyrus R. Mehta & Nitin R. Patel (1986). Algorithm 643. FEXACT: A Fortran subroutine for Fisher's exact test on unordered r*c contingency tables. ACM Transactions on Mathematical Software, 12, 154𤪑.
Douglas B. Clarkson, Yuan-an Fan & Harry Joe (1993). A Remark on Algorithm 643: FEXACT: An Algorithm for Performing Fisher's Exact Test in r x c Contingency Tables. ACM Transactions on Mathematical Software, 19, 484𤯘.