[R-meta] Back transformation of arcsine transformed data in meta-regression

[Guido Schwarzer]

Daniel,

The maximum value you can get for arcsine transformed proportions is 
1.571 (for a proportion of 100%) which you can see using the following R 
command: asin(sqrt(1))

Accordingly, the intercept 3.06 in your meta-regression is way of the 
mark due to extrapolating the effect of the continuous variable year. 
The intercept represents the effect at year 0 A.D.

I would suggest that you center the variable year around some value.

Best wishes, Guido

-- 
Dr. Guido Schwarzer
Institute of Medical Biometry and Statistics,
Faculty of Medicine and Medical Center - University of Freiburg

Postal address: Stefan-Meier-Str. 26, D-79104 Freiburg

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