Line luminosities as a function of accretion luminosity. Top: diagnostic water lines. Bottom: HCN, C₂H₂, and CO₂. The Class I/FS and II samples generally follow the same trends, but Class I/FS shows larger scatter in the water lines. The gray dashed line and shaded band show the censored linmix fit (B. C. Kelly 2007) to the Class II reference sample (16th–84th percentile of the posterior), which includes the upper limits; a separate Class I/FS linmix fit is not shown because too few Class I/FS sources have L_acc detections. The generalized (censored) Kendall τ and its p-value are annotated in each panel for the Class II (τ_II) and Class I/FS (i < 70^∘; τ_I) samples, computed separately so the two trends can be compared.