ttest.tstat: Use t statistic to compute Bayes factor for one- and two-...

Description Usage Arguments Details Value Author(s) References See Also Examples

View source: R/ttest_tstat.R

Description

Using the classical t test statistic for a one- or two-sample design, this function computes the corresponding Bayes factor test.

Usage

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  ttest.tstat(t, n1, n2 = 0, nullInterval = NULL,
    rscale = "medium")

Arguments

t

classical t statistic

n1

size of first group (or only group, for one-sample tests)

n2

size of second group, for independent-groups tests

nullInterval

optional vector of length 2 containing lower and upper bounds of an interval hypothesis to test, in standardized units

rscale

numeric prior scale

Details

This function can be used to compute the Bayes factor corresponding to a one-sample, a paired-sample, or an independent-groups t test, using the classical t statistic. It can be used when you don't have access to the full data set for analysis by ttestBF, but you do have the test statistic.

For details about the model, see the help for ttestBF, and the references therein.

The Bayes factor is computed via Gaussian quadrature.

Value

If nullInterval is defined, then two Bayes factors will be computed: The Bayes factor for the interval against the null hypothesis that the standardized effect is 0, and the corresponding Bayes factor for the compliment of the interval. For each Bayes factor, a vector of length 2 containing the computed log(e) Bayes factor (against the point null), along with a proportional error estimate on the Bayes factor is returned.

Author(s)

Richard D. Morey ([email protected]) and Jeffrey N. Rouder ([email protected])

References

Morey, R. D. & Rouder, J. N. (2011). Bayes Factor Approaches for Testing Interval Null Hypotheses. Psychological Methods, 16, 406-419

Rouder, J. N., Speckman, P. L., Sun, D., Morey, R. D., & Iverson, G. (2009). Bayesian t-tests for accepting and rejecting the null hypothesis. Psychonomic Bulletin & Review, 16, 752-760

See Also

integrate, t.test; see ttestBF for the intended interface to this function, using the full data set.

Examples

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## Classical example: Student's sleep data
data(sleep)
plot(extra ~ group, data = sleep)

## t.test() gives a t value of -4.0621
t.test(extra ~ group, data = sleep, paired=TRUE)
## Gives a Bayes factor of about 17
## in favor of the alternative hypothesis
result <- ttest.tstat(t = -4.0621, n1 = 10)
exp(result[['bf']])

Example output

Loading required package: coda
Loading required package: Matrix
************
Welcome to BayesFactor 0.9.12-2. If you have questions, please contact Richard Morey (richarddmorey@gmail.com).

Type BFManual() to open the manual.
************

	Paired t-test

data:  extra by group
t = -4.0621, df = 9, p-value = 0.002833
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 -2.4598858 -0.7001142
sample estimates:
mean of the differences 
                  -1.58 

[1] 17.25829

BayesFactor documentation built on May 31, 2017, 4:17 a.m.