Pearson's Chi-square Test for Count Data
Usage
chisq.test(x, y = NULL, correct = TRUE,
p = rep(1/length(x), length(x)))
Arguments
x
|
a vector or matrix.
|
y
|
a vector; ignored if x is a matrix.
|
correct
|
a logical indicating whether to apply continuity
correction when computing the test statistic.
|
Description
chisq.test performs chi-square tests on contingency tables.Details
If x is a matrix with one row or column, or if x is a
vector and y is not given, x is treated as a
one-dimensional contingency table. In this case, the hypothesis
tested is whether the population probabilities equal those in
p, or are all equal if p is not given.
If x is a matrix with at least two rows and columns, it is
taken as a two-dimensional contingency table, and hence its entries
should be nonnegative integers. Otherwise, x and y
must be vectors or factors of the same length; incomplete cases are
removed, the objects are coerced into factor objects, and the
contingency table is computed from these. Then, Pearson's
chi-square test of the null that the joint distribution of the cell
counts in a 2-dimensional contingency table is the product of the row
and column marginals is performed. Continuity correction is only
used in the 2-by-2 case if correct is TRUE.
Value
A list with class "htest" containing the following
components:
statistic
|
the value the chi-square test statistic.
|
parameter
|
the degrees of freedom of the approximate
chi-square distribution of the test statistic.
|
p.value
|
the p-value for the test.
|
method
|
a character string indicating the type of test
performed, and whether continuity correction was used.
|
data.name
|
a character string giving the name(s) of the data.
|
observed
|
the observed counts.
|
expected
|
the expected counts under the null hypothesis.
|
Examples
data(insects) # Not really a good example
chisq.test(insects$count > 7, insects$spray)
# Prints test summary
chisq.test(insects$count > 7, insects$spray)$obs
# Counts observed
chisq.test(insects$count > 7, insects$spray)$obs
# Counts expected under the null