Hi R-users,
I have a fairly simple question to ask but I havent yet got an answer to the
question. I will describe my experiment, analysis and what have I done and what
is the question in the following paragraphs and I would appreciate if anyone
could point me to use right statistical tools to answer my question.
Experiment:
I have 2 groups and both groups undergo 2 set of evaluations, one with MRI
scanner and the other in the lab to test for their behavior. Both these
evaluations are known to have statistically significant relationship with age
and gender.
Statistical question of interest:
Whether there is:
1) statistically significant difference between the 2 groups on each evaluation
?
2) Whether there is any relationship between and within the 2 groups between
each evaluation
Model:
I model the problem as following:
MRI_measure = Intercept + Slope1 * Age + Slope 2 * Gender + Slope3 * Group [Age
is continuous and gender , Group are factors/categorical]
Lab_measure = Intercept + Slope1 * Age + Slope 2 * Gender + Slope3 * Group [Age
is continuous and gender , Group are factors/categorical]
In order to obtain the solution in R:
MRI_model<-lm(cbind(MRI_measure, Lab_measure) ~ age+gender+group, data=data)
Result of R:
manova(MRI_model) suggests that yes indeed all the slopes are significantly
different than 0 suggesting a relationship between my measures.
Question:
1) In order to test whether the difference in the MRI_measure is statistically
significant different between the 2 groups, I use MRI_model$fitted.values for
each dependent measure and do a statistical test (either t-test or Wilcox) and
claim that the difference is significant.
In the paper I write, multivariate multiple linear regression was performed for
the groups while controlling for age and gender. The regressed out MRI_measure
was statistically compared to see if the difference is different.
I am assuming that the predicted/fitted.values in model are the regressed out
variables. Can I show this and use this result? Is this right
If no, what is the correct way to statistically compare whether my 2 groups
differ in their MRI measure and lab measure when controlled for age and gender.
Any R library, literature, possibly a script will be greatly appreciated.
2) I also want to see if there is any relationship between MRI_measure and
Lab_measure within the group after they are controlled for age and gender. What
is the correct way to do this in R?
Further, I also want to see if there is any significantly different association
between the 2 groups for my set of dependent variables. I am thinking this can
be done: I first find the correlation between 2 dependent variable in each
group and test if this correlation is statistically different between the 2
groups? Is this logic right? And if it is, how do I compare the correlation? If
not, what is the right way to do this? Any R library, literature, possibly a
script will be greatly appreciated.
I do appreciate any reply.
Thanks
Regards
Virendra
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