Kendall’s τ_b rank correlation coefficients between the expansion velocity (v_exp), pulsation period (P), mass-loss rate , effective temperature (T_eff), and number of detected lines of various molecules in each source. Correlation coefficients with 3σ significance are in boldface, 2σ in regular font, and 1σ in small italics. Coefficients with lower than 1σ significance are not included, and instead given as - - The cells are colorized from perfect correlation (1) in blue, to perfect anti-correlation (−1) in red.