Probability distribution of the gap size (measured with its outer edge) and accretion rate (measured at 1.5 AU) for a population synthesis model with (top) and without (bottom) a dead zone. The dead zone model uses r_dz = 10 AU and α_dz = 10⁻⁴. Disks with accretion rates lower than 10⁻¹² M_⊙ yr⁻¹ are counted in the lowest accretion-rate bin. The gray dots mark the observed population of transition disks compiled in the Ercolano & Pascucci (2017) review. The dots with arrows mark upper limits in the accretion rate.