Ratio of the PAH-to-dust mass fraction to the PAH-to-total IR luminosity fraction versus the PAH mass fraction in our sample. Both quantities are derived from the Draine & Li (2007) models (Section 2.3). Robust q_PAH sample shows galaxies with q_PAH with > 3σ significance or less than 0.5% error (Section 2.2). Left: PAH luminosity fraction is defined as the ratio of the PAH 7.7 μm feature luminosity to total IR luminosity. Horizontal line is the unity line. The robust sample is fit with a polynomial function shown with a dashed curve (Equation (1)). Right: PAH luminosity is the sum of the 3.3, 6.2, 7.7, 11.2, and 17 μm PAH features luminosities (Section 2.3.1). Horizontal line shows the median of the robust sample (0.68). We note that q_PAH is not in percentage units, unlike the other figures in this paper.