| prop.test {base} | R Documentation |
Test for Equal or Given Proportions
Description
prop.test can be used for testing the null that the
proportions (probabilities of success) in several groups are the
same, or that they equal certain given values.
Usage
prop.test(x, n = NULL, p = NULL, alternative = "two.sided",
conf.level = 0.95, correct = TRUE)
Arguments
x |
a vector of counts of successes or a matrix with 2 columns giving the counts of successes and failures, respectively. |
n |
a vector of counts of trials; ignored if |
p |
a vector of probabilities of success. The length of
|
alternative |
indicates the alternative hypothesis and must be
one of |
conf.level |
confidence level of the returned confidence interval. Must be a single number between 0 and 1. Only used when testing the null that a single proportion equals a given value, or that two proportions are equal; ignored otherwise. |
correct |
a logical indicating whether Yates' continuity correction should be applied. |
Details
Only groups with finite numbers of successes and failures are used. Counts of successes and failures must be nonnegative and hence not greater than the corresponding numbers of trials which must be positive. All finite counts should be integers.
If p is NULL and there is more than one group, the
null tested is that the proportions in each group are the same. If
there are two groups, the alternatives are that the probability of
success in the first group is less than, not equal to, or greater
than the probability of success in the second group, as specified by
alternative. A confidence interval for the difference of
proportions with confidence level as specified by conf.level
and clipped to [-1,1] is returned. Continuity correction is
used only if it does not exceed the difference of the sample
proportions in absolute value. Otherwise, if there are more than 2
groups, the alternative is always "two.sided", the returned
confidence interval is NULL, and continuity correction is
never used.
If there is only one group, then the null tested is that the
underlying probability of success is p, or .5 if p is
not given. The alternative is that the probability of success if
less than, not equal to, or greater than p or 0.5,
respectively, as specified by alternative. A confidence
interval for the underlying proportion with confidence level as
specified by conf.level and clipped to [0,1] is
returned. Continuity correction is used only if it does not exceed
the difference between sample and null proportions in absolute
value.
Finally, if p is given and there are more than 2 groups, the
null tested is that the underlying probabilities of success are
those given by p. The alternative is always
"two.sided", the returned confidence interval is NULL,
and continuity correction is never used.
Value
A list with class "htest" containing the following
components:
statistic |
the value of Pearson's chi-square test statistic. |
parameter |
the degrees of freedom of the approximate chi-square distribution of the test statistic. |
p.value |
the p-value of the test. |
estimate |
a vector with the sample proportions |
conf.int |
a confidence interval for the true proportion if
there is one group, or for the difference in proportions if
there are 2 groups and |
null.value |
the value of |
alternative |
a character string describing the alternative. |
method |
a character string indicating the method used, and whether Yates' continuity correction was applied. |
data.name |
a character string giving the names of the data. |
Examples
heads <- rbinom(1, size=100, pr = .5)
prop.test(heads, 100) # continuity correction TRUE by default
prop.test(heads, 100, correct = FALSE)
## Data from Fleiss (1981), p. 139.
## H0: The null hypothesis is that the four populations from which
## the patients were drawn have the same true proportion of smokers.
## A: The alternative is that this proportion is different in at
## least one of the populations.
smokers <- c( 83, 90, 129, 70 )
patients <- c( 86, 93, 136, 82 )
prop.test(smokers, patients)