To test if this explains the improved performance, we compared multilingual and bilingual models under similar data size conditions, i.e., the total parallel corpora size across all language pairs used to train the multilingual model is equivalent to the size of the bilingual corpus used to train the bilingual model.
we compared the following under similar data size conditions: (a) {bn,hi,kn,ta}-en multilingual model (50% hi-en training pairs) with hi-en bilingual model (b) {cs,pl,sk,sl}-ar multilingual model (30% pl-ar training pairs) with pl-ar bilingual model.