G.bintest function

G-test for binary variables

Performs a G-test for comparing response probabilities (i.e. when the response variable is a binary variable). The function is in fact a wrapper to the G-test for comparison of proportions on a contingency table. If the p-value of the test is significant, the function performs pairwise comparisons by using G-tests.

G.bintest(formula, data, alpha = 0.05, p.method = "fdr")

Arguments

• formula: a formula of the form a ~ b, where a and b give the data values and corresponding groups, respectively. a can be a numeric vector or a factor, with only two possible values (except NA).
• data: an optional data frame containing the variables in the formula formula. By default the variables are taken from environment(formula).
• alpha: significance level to compute pairwise comparisons.
• p.method: method for p-values correction. See help of p.adjust.

Details

If the response is a 0/1 variable, the probability of the '1' group is tested. In any other cases, the response is transformed into a factor and the probability of the second level is tested.

Since a G-test is an approximate test, an exact test is preferable when the number of individuals is small (200 is a reasonable minimum). See fisher.bintest in that case.

Returns

• method.test: a character string giving the name of the global test computed.

• data.name: a character string giving the name(s) of the data.

• alternative: a character string describing the alternative hypothesis.

• estimate: the estimated probabilities.

• null.value: the value of the difference in probabilities under the null hypothesis, always 0.

• statistic: test statistics.

• parameter: test degrees of freedom.

• p.value: p-value of the global test.

• alpha: significance level.

• p.adjust.method: method for p-values correction.

• p.value.multcomp: data frame of pairwise comparisons result.

• method.multcomp: a character string giving the name of the test computed for pairwise comparisons.

Author(s)

Maxime HERVE maxime.herve@univ-rennes1.fr

See Also

chisq.bintest, fisher.bintest

Examples

response <- c(rep(0:1,c(40,60)),rep(0:1,c(55,45)),rep(0:1,c(65,35)))
fact <- gl(3,100,labels=LETTERS[1:3])
G.bintest(response~fact)