Description Usage Arguments Details Author(s) References Examples
Returns a t-value based on the given contrast weights Same as yuen.contrast (see Ryne's code, not implemented in russmisc) only no trimming is allowed. Created largely for sanity checks, yuen.contrast should generally be used.
1 2 3 4 5 |
DV |
A numeric vector of the same length as IV containing the measured values. |
IV |
A factor of the same length as DV containing the independent variable codes. |
wgt |
A numeric vector containing the contrast
weights corresponding to each successive level of the IV.
If this value is left NULL, the function will try to use
the |
alpha |
A numeric element > .00 and < 1.00 specifying the Type I error rate. |
EQVAR |
A logical indicating whether equal variances amongst the groups should be assumed. |
alternative |
A character vector specifying the alternative hypothesis. Must be one of "unequal", "greater", or "less". |
x |
an object used to select the method. |
... |
further arguments passed to or from other methods. |
This function computes a t-value for a DV given a set of
contrast weights following Rosenthal, Rosnow, & Rubin
(2000). If EQVAR=FALSE then degrees of freedom are
calculated using Welch's method. The wgt option allows
one to specify contrast weights to test hypotheses with
more than 2 levels of an IV. By default it tests the
hypothesis that the sum of the wgt vector times the DV
means for each IV is greater than 0. To get a two-tailed
p-value or one predicting a negative contrast, change the
alternative
parameter.
Ryne Sherman <rsherm13@fau.edu>; modifications by Russell S. Pierce <rpier001@ucr.edu>
Rosenthal, R., Rosnow, R.L., & Rubin, D.B. (2000).
Contrasts and effect sizes in behavioral research:
A correlational approach. New York: Cambridge University
Press.
Rosenthal, R., Rosnow, R.L., & Rubin, D.B.
(2000). Contrasts and correlations in effect-size
estimation. Psychological science. 11(6),
446-453.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | # To test a single contrast...
tContrast(warpbreaks$breaks,warpbreaks$tension,wgt=c(-1,0,1))
# To test multiple contrasts...
# We make a matrix with our desired contrasts
my.contr <- cbind(
I = c(-1,0,1),
II = c(1,0,-1),
III = c(1,-2,1)
)
# Now we set the contrasts along side the variable
# Now we have to change how.many to match the number
# of contrasts we have
contrasts(warpbreaks[,"tension"],how.many=3) <- my.contr # set the contrasts for the 'group' factor
tContrast(warpbreaks$breaks,warpbreaks$tension)
|
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