conversion functions

These are a number of functions to convert statistics and effect size measures from/to each other.

Arguments

chisq, cohensf, cohensfsq, d, etasq, f, logodds, means, omegasq, or, p, r, t, z

The value of the relevant statistic or effect size.

ncf

The value of a noncentrality parameter of the F distribution.

n, n1, n2, N, ns

The number of observations that the r or t value is based on, or the number of observations in each of the two groups for an anova, or the total number of participants when specifying a noncentrality parameter.

df, df1, df2

The degrees of freedrom for that statistic (for F, the first one is the numerator (i.e. the effect), and the second one the denominator (i.e. the error term).

proportion

The proportion of participants in each of the two groups in a t-test or anova. This is used to compute the sample size in each group if the group sizes are unknown. Thus, if you only provide df1 and df2 when converting an F value to a Cohen's d value, equal group sizes are assumed.

b

The value of a regression coefficient.

se, sds

The standard error of standard errors of the relevant statistic (e.g. of a regression coefficient) or variables.

minDim

The smallest of the number of columns and the number of rows of the crosstable for which the chisquare is translated to a Cramer's V value.

lower.tail

For the F and chisquare distributions, whether to get the probability of the lower or upper tail.

akfEq8

When converting Cohen's d to r, for small sample sizes, bias is introduced when the commonly suggested formula is used (Aaron, Kromrey & Ferron, 1998). Therefore, by default, this function uses different equations depending on the sample size (for n < 50 and for n > 50). When akfEq8 is set to TRUE or FALSE, the corresponding action is taken; when akfEq8 is not logical (i.e. TRUE or FALSE), the function depends on the sample size.

var.equal

Whether to compute the value of t or Cohen's d assuming equal variances ('yes'), unequal variances ('no'), or whether to test for the difference ('test').

Value

The converted value as a numeric value.

Details

Note that by default, the behavior of convert.d.to.r depends on the sample size (see Bruce, Kromrey & Ferron, 1998).

References

Aaron, B. Kromrey J. D. & Ferron, J. (1998) Equating "r"-based and "d"-based Effect Size Indices: Problems with a Commonly Recommended Formula. Paper presented at the Annual Meeting of the Florida Educational Research Association (43rd, Orlando, FL, November 2-4, 1998).

Author

Gjalt-Jorn Peters and Peter Verboon

Maintainer: Gjalt-Jorn Peters gjalt-jorn@userfriendlyscience.com

Examples

convert.t.to.r(t=-6.46, n=200);
#> [1] -0.4172246
convert.r.to.t(r=-.41, n=200);
#> [1] -6.325297

### Compute some p-values
convert.t.to.p(4.2, 197);
#> [1] 4.041281e-05
convert.chisq.to.p(5.2, 3);
#> [1] 0.3154489
convert.f.to.p(8.93, 3, 644);
#> [1] 1.6762e-05

### Convert d to r using both equations
convert.d.to.r(d=.2, n1=5, n2=5, akfEq8 = FALSE);
#> [1] 0.09950372
convert.d.to.r(d=.2, n1=5, n2=5, akfEq8 = TRUE);
#> [1] 0.1111111