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[R-meta] converting escalc ROM outputs to the log-2 scale

4 messages · Divya Ravichandar, Wolfgang Viechtbauer

Divya Ravichandar
# 
Hi all

I have a question around changing the scale of *yi *and *vi *exported
from *escalc()
*function when using *measure=ROM.* Based on the documentation, this
function exports *yi *in natural log (ln) scale. --> yi =
ln(grp1-mean/grp2-mean) and then the associated vi.

I am interested in obtaining the *log-2 fold change. *Is there a way to
convert yi & vi from *escalc(measure = ROM,...) *to this scale. Would it be
reasonable to simply transform the values by converting from log-e -> log-2
scale by
yi_new = yi/log(2) and vi_new = vi/log(2)

Thank you
Wolfgang Viechtbauer
# 
Dear Divya,

If y_i ~ N(theta_i, v_i), then for any constant c, c*y_i ~ N(c*theta_i, c^2 * v_i).

So, it would be yi_new = yi/log(2) and vi_new = vi/log(2)^2.

Best,
Wolfgang
Divya Ravichandar
# 
Hi Dr. Wolfgang

Thank you for getting back to me. Could you help me understand more on why
we square the log(2) in the vi calculation?



On Fri, Dec 11, 2020 at 6:37 PM Viechtbauer, Wolfgang (SP) <
wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    
5 days later

    

      
      

        


  

        

      Wolfgang Viechtbauer
    

    

      
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Dear Divya,

That's just how variances change under multiplicative transformations. The same works with raw data:

x <- rnorm(10)
var(x)
var(2*x)
2^2 * var(x)

Best,
Wolfgang