On 20/10/15 01:02, Dr. Leigh S. Sutherland wrote:
Still feeling my way around using R...
What I have done so far:
I have a data.frame 'results' with response 'Fail', and three factors
'PREP', 'CLEAN' & 'ADHES'. ADHES has 3 levels: Crest Cryst Poly
I calculated the variances:
sigma..k=tapply(Fail,ADHES,var)
print(sqrt(sigma..k)):
Crest Cryst Poly 17.56668 41.64679 39.42669
then used leveneTest to test for constance of variance:
print(leveneTest(Fail~ADHES))
How does leveneTest() find the variables "Fail" and "ADHES" given that
you do not provide it with a "data" argument?
Levene's Test for Homogeneity of Variance (center = median)
Df F value Pr(>F)
group 2 3.929 0.02588 *
51
The Question:
Now I want to use Levene's to test for constance of variance between only
the Cryst & Poly levels of the factor ADHES, but I cant work out the syntax
to do this in R.
Could anyone help, please?
I am not at all sure that I understand your somewhat incoherently
expressed question, but I *think* that what you want to do might be done
by setting
ok <- with(results,ADHES%in%c("Cryst","Poly"))
leveneTest(Fail ~ ADHES, data=results[ok,])
It's hard to say, since you do not provide a reproducible example.
cheers,
Rolf Turner
--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276
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