Depicted is OPG- rs1485305 in the Leiden-EAC (A) and in the meta-analysis on all data-sets (B). SHS = Sharp-van der Heijde score. The effect sizes are the estimated relative progression rates per year for the presence of the minor allele for OPG compared to patients without the minor allele. A) The presence of the minor variant of OPG-1485305 (T) is associated with a 1.03 fold rate of joint destruction per year compared to patients with the common genotypes in the Leiden-EAC. Since the effect sizes increases by the power of the number of follow-up years, these patients have a 1.23 (1.03^7) fold rate of joint destruction over 7-years, in other words a 23% higher rate of joint destruction. B) The meta-analysis is based on a fixed effect model, which is applied to genetic studies to test whether there is statistically significant effect; generalizability of the effect is of less importance. Consequently, this method is less suitable to estimate the effect size overall. Therefore, the estimated effect of the meta-analysis is depicted in gray. The I2 was 13.6% and the p-value for heterogeneity was 0.325. The p-value for a random model was 0.004 and the effect size 1.23 (see also Additional file 3: Table S3).