I am trying to understand a GWAS paper which reports the effect of a SNP on outcome as a % variation, e.g., 15% variation in xxx levels.

The only information reported are the beta, standard error and p-values. I tried to read the paper but there is no mention of how this is calculated.

The paper in question is <a href="http://hmg.oxfordjournals.org/content/18/14/2700.abstract?ijkey=6a56a8fcc46b8f6ff554ee3f87d5d316cc0a0f4e&keytype2=tf_ipsecsha">Genome-wide association meta-analysis for total serum bilirubin levels</a> (Hum. Mol. Genetics, 2009).

Paragraph in question = These SNPs accounts for approximately 17.5, 18.1 and
16.7% of the variation...

If anyone has any clue, please help. I'll be most appreciative.