Diving into the numbers, Dobrynskaya and Kishilova discovered that certain LEGO set characteristics resulted in higher or lower returns. Small sets with an average of 113 pieces and huge sets with over 3,000 pieces earned more than medium-sized sets. Some themes also increased in value more than others.

“LEGO Ideas and Seasonal sets yield the highest returns on the secondary market,” the researchers wrote. “Sets which follow popular movies are also attractive. The least attractive themes seem to be the ones which stopped being released before 2010. Perhaps, the company stopped producing them because of low popularity on the primary market.”