Hi jacaranda,
Try
with(subset(mydata, Group1 == 1), cor.test(Gen, MSELEL, method = "pearson"))
HTH,
Jorge.-
On Sun, Jun 3, 2012 at 11:51 AM, jacaranda tree <> wrote:
> Hi all,
> I started using R about 3 weeks ago, and now I've pretty much figured out
> how to do the types of statistical modeling, graphs, tables etc. that I
> frequently use (with zero background in computer languages or other
> statistical packages that are similar to R like S or SAS!). So it's been a
> quite rewarding process so far, and I thank you all R gurus for all your
> generous help!
> That being said, my question is about applying a model or an analysis to
> different groups based on a grouping variable. Below is the first six rows
> of my data:
>
> ID Group1 Group2 Mem Gen Chance MSELGM MSELVR MSELFM MSELRL MSELEL
> ADOS Age
> 1 1 1 1 75 50.0 50 53
> 52 62 57 56 3 25
> 2 2 1 1 75 12.5 50 46
> 48 47 52 55 2 30
> 3 3 1 1 25 37.5 50 48
> 43 52 63 63 3 24
> 4 4 1 1 25 37.5 50 51
> 62 52 59 54 0 31
> 5 5 1 1 50 87.5 50 45
> 58 42 46 43 6 31
> 6 6 1 1 100 100.0 50 45
> 80 49 69 63 1 31
>
> Group1: First grouping variable
> Group2: Second grouping variable
> Mem: Memory trial
> Gen: Generalization trial
> MSEL: Mullen Scales of Early Learning (a scale measuring various skills in
> little children). GM: Gross Motor Scale, VR: Visual Reception, FM: Fine
> Motor, RL: receptive Language, EL: Expressive Language.
> ADOS: An autism-specific measure.
>
> First I wanted to do correlations between Generalization (variable Gen)
> and expressive language (MSELEL) for each group of Group1. For this, I used
> lapply or by functions which work just fine. Here is the code with
> lapply: lapply(split(mydata, mydata$Group1), function(x){cor.test(x[,5],
> x[,11], method = "pearson")})
>
> Then I did regression. My DV is the variable Gen, and the IV is MSELEL.
> And again I wanted to do this for each group. Here is the code I came up
> with for each group:
> fit1<-lm(Gen~ MSELEL, data=mydata, subset=mydata$Group1==1)
>
> fit2<-lm(Gen~MSELEL, data=mydata, subset=mydata$Group1==2)
>
> This works fine for regression, but when I used the "subset" function with
> the correlation (e.g. cor.test (mydata$Gen, mydata$MSELEL,
> method="pearson", subset=mydata$Group1==1) , it did not work. It just did
> the correlation for the entire group and then used this for both groups. I
> was just curious as to why subset function works with regression, but not
> with correlation. Any thoughts?
> Thanks,
> [[alternative HTML version deleted]]
>
>
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>
>
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