[R] a pickle (solved first part now need r's from data)

John Christie jc at or.psychology.dal.ca
Fri Aug 22 14:18:15 CEST 2003

On Friday, August 22, 2003, at 01:44  AM, John Christie wrote:

> I predicted that y would increase as x increased.  However, I only 
> made the prediction on the ranks of the scores.  The ranks don't 
> correlate with predicted.  And, I don't think a regression on the 
> ranks is warranted.  However, the actual scores do yield a significant 
> slope for b, and a significant R^2 using a linear regression (y is the 
> value and x is the predicted rank).  What should my argument be here?  
> Should I have endorsed using the actual scores instead of ranks to 
> begin for some reason that doesn't have anything to do with my current 
> result? :)

OK, now I realize that I should probably not have been correlating 
ranks in the first place because my real data may have had a 
non-linear, but still steadily increasing, slope.  The ranks would tend 
to increase variance where the slope was low and ruined my chance of 
finding an effect.

> Oh, on another note, I can use rcorr to get the Spearman correlations, 
> but I'd like to be able to just add
> the ranks as a column.  I was going to just use order and add a simple 
> factor.  But, that doesn't deal with ties correctly.

still don't have these yet.

> And, I also wanted to analyze correlations subject by subject and 
> compare my two groups.  However, there doesn't seem to be a good way 
> to get this.  I tried using "by" with "cor".  However, this requires 
> binding x and y which causes cor to return a matrix (if you could pass 
> it x and y separate it would just return a number).
> given
> data frame s
> x	y	subj
> 4	7	harry
> 5	1	harry
> 6	9	harry
> 2	4	steve
> 3	7	steve
> ...
> i'd like to be able to produce
> r	subj
> .12	harry
> .52	steve
> ...
> any tips?

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