Calculated molecular line ratios of c-C₃H₂ (top row), H₂CO (second row), DCO⁺ (third row) and ¹³CO (bottom row) compared to the system parameters bolometric luminosity L_bol (left column), envelope mass M_env (middle column), and the mass to luminosity ratio M_env∕L_bol (right column). The black and red dashed lines in the top row are linear fits to the data for the 6–5/3_3,0–2_2,1 and 5_1,4–4_2,3/3_3,0–2_2,1 ratios, respectively. Circles, diamonds, and stars show single, close binary, and wide multiple protostellar systems, respectively. The c-C₃H₂ ratios appear to be somewhat related to luminosity, whereas the ratios from H₂ CO and DCO⁺ are constantregardless of system parameter.