We measure the differential microlensing of the broad emission lines between 18 quasar image pairs in 16 gravitational lenses .
We find that the broad emission lines are in general weakly microlensed .
The results show , at a modest level of confidence ( 1.8 \sigma ) , that high ionization lines such as CIV are more strongly microlensed than low ionization lines such as H \beta , indicating that the high ionization line emission regions are more compact .
If we statistically model the distribution of microlensing magnifications , we obtain estimates for the broad line region size of r _ { s } = 24 _ { -15 } ^ { +22 } and r _ { s } = 55 _ { -35 } ^ { +150 } light-days ( 90 % confidence ) for the high and low ionization lines , respectively .
When the samples are divided into higher and lower luminosity quasars , we find that the line emission regions of more luminous quasars are larger , with a slope consistent with the expected scaling from photoionization models .
Our estimates also agree well with the results from local reveberation mapping studies .