t.test.ratio {mratios} | R Documentation |
Performs t-test for the ratio of means of independent samples from two gaussian distributions. In case of heterogeneous variances a Satterthwaite approximation of the degrees of freedom is used (Tamhane & Logan, 2004).
t.test.ratio(x, ...) ## Default S3 method: t.test.ratio(x, y, alternative = "two.sided", rho = 1, var.equal = FALSE, conf.level = 0.95, ...) ## S3 method for class 'formula': t.test.ratio(formula, data, base=2, ...)
x |
A numeric vector (group in the numerator of the ratio) |
y |
A numeric vector (group in the denominator of the ratio) |
formula |
A two-sided formula specifying a numeric response variable and a factor with two levels |
data |
A dataframe containing the variables specified in formula. Note: the first group in alpha-numeric order will appear in the denominator of the ratio |
alternative |
character string defining the alternative hypothesis, one of "two.sided", "less" or "greater" |
rho |
a single numeric value: the margin or ratio under the null hypothesis |
var.equal |
logical, if set TRUE, a ratio-t-test assuming equal group variances is performed, otherwise (default) unequal variances are assumed |
conf.level |
confidence level of Fieller's interval for the ratio of two means |
base |
if formula is used: a single numeric value specifying whether the first or second group (according to alpha-numeric order) is to be used as denominator |
... |
arguments to be passed to t.test.ratio.default |
An object of class "htest"
Frank Schaarschmidt
Kieser, M., Hauschke, D. (2000): Statistical methods for demonstrating equivalence in crossover trials based on the ratio of two location parameters. Drug Information Journal 34, 563-568.
Tamhane, A.C., Logan, B.R. (2004): Finding the maximum safe dose level for heteroscedastic data. Journal of Biopharmaceutical Statistics 14, 843-856.
# # # ASAT values of female rats in a toxicity study (Hauschke, 1999). data(ASAT) ASAT t.test.ratio(ASAT~group, data=ASAT, alternative="less", base=1, rho=1.25, var.equal=TRUE) # # # Bodyweights of male rats in a toxicity study. Objective was to show equivalence between the high dose group (Dosis) and the control group (Kon). # Equivalence margins are set to 0.8 and 1.25. The type-I-error to show equivalence is set to alpha=0.05. data(rat.weight) # two one-sided tests: t.test.ratio(weight~group, data=rat.weight, alternative="less", rho=1.25, var.equal=TRUE) t.test.ratio(weight~group, data=rat.weight, alternative="greater", rho=0.8, var.equal=TRUE) # # # for rho=1, t.test.ratio corresponds to a simple t.test with the difference of means under the null set to zero (,i.e. mu=0). t.test.ratio(ASAT~group, data=ASAT, alternative="less", rho=1, var.equal=TRUE) t.test(ASAT~group, data=ASAT, alternative="less", mu=0, var.equal=TRUE)