ANOVA/statistics question
Hello again, In my situation, I have three variables: pretest, posttest, and cohesion. I want to work out the correlation between postest and cohesion. I looked at multiple sets of data and created ANOVA tables of them. However, as pretest and postest are sometimes correlated (with a statistical significance < 0.05), it is necessary to discount the effect of pretest to work out the real correlation of posttest and coherence.. I need a system for working out the strength of the correlation between posttest and coherence, when does actually occur. According to my understanding level refers the amount or magnitude of experimental units. Pretest, posttest are scores - range from any value from 0 to 1. Cohesion can be any value. What exactly would cor(y[pre == 1], x[pre == 1]) cor(y[pre == 2], x[pre == 2]) give me? I understand that my lack of understanding may be exasperating, but it is not for want of effort - I have put in hours trying to understand this stuff. Thanks, Douglas Holmes
Tal Galili wrote:
Hi Douglas. So you want to check for correlation or regression ? how many levels does "pre" have ? you could subset the variables you want to check correlation on, by the pre levels. for example: Let's say pre has two levels: 1 and 2. then you can do: cor(y[pre == 1], x[pre == 1]) cor(y[pre == 2], x[pre == 2]) Also, If you want to go for regression, you can go to something like: summary(lm(y ~ x + pre)) But I suggest getting much more understanding of what linear regression is before using it's methods... Good luck, Tal On Sat, Apr 25, 2009 at 1:26 PM, drmh <douglasrmholmes at googlemail.com>wrote:
Hi, thanks for your prompt reply In my situation, the dependent variable is "post-test" and the independent variables are "pre" and "coh". Howw would I find the correlation between coh and post with the effect of "pre" regressed using your commands? Tal Galili wrote:
Hi Douglas I would go for a different command then aov. something like: ?cor or ?cor.test To also get the p value of the correlation. Cheers, Tal On Sat, Apr 25, 2009 at 8:27 AM, drmh <douglasrmholmes at googlemail.com>wrote:
(Have searched for this already) Hi, How do you find the strength of correlation between two variables
using
an
ANOVA table? "Pr(>F)" gives the statistical significance of the
association, but not the strength of the correlation.
See data (from R) below
Readable:
"Df" "Sum Sq" "Mean Sq" "F
value"
"Pr(>F)"
"pre" 1 0.00593 0.00593936
0.7450563 0.401636958677004
"coh" 1 0.04311 0.04311302
5.4082639
0.0344751749542619
"Residuals" 15 0.11957 0.00797169 NA
NA
Original:
"Df" "Sum Sq" "Mean Sq" "F value" "Pr(>F)"
"pre" 1 0.0059393604629317 0.0059393604629317 0.745056336657567
0.401636958677004
"coh" 1 0.0431130207164516 0.0431130207164516 5.40826398359156
0.0344751749542619
"Residuals" 15 0.119575396598395 0.00797169310655964 NA NA
Any help would be greatly appreciated,
Douglas Holmes
--
View this message in context:
Sent from the R help mailing list archive at Nabble.com.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
-- ---------------------------------------------- My contact information: Tal Galili Phone number: 972-50-3373767 FaceBook: Tal Galili My Blogs: http://www.r-statistics.com/ http://www.talgalili.com http://www.biostatistics.co.il [[alternative HTML version deleted]]
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
-- View this message in context: http://www.nabble.com/ANOVA-statistics-question-tp23231563p23234421.html Sent from the R help mailing list archive at Nabble.com.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
-- ---------------------------------------------- My contact information: Tal Galili Phone number: 972-50-3373767 FaceBook: Tal Galili My Blogs: http://www.r-statistics.com/ http://www.talgalili.com http://www.biostatistics.co.il [[alternative HTML version deleted]]
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
View this message in context: http://www.nabble.com/ANOVA-statistics-question-tp23231563p23242901.html Sent from the R help mailing list archive at Nabble.com.