Distribution of R_PAH^* for resolved (luminous) H II regions (orange) and the regions of similar size from the diffuse ISM (blue) for several gas-phase metallicity bins. The one dashed line and the two dotted lines on each distribution show the median and 25 and 75 percentile quartiles, respectively. Both R_PAH and R_PAH^* are lower in the H II regions than in the diffuse ISM. A strong decrease in R_PAH^* in the lowest metallicity bin is seen for the H II regions and the diffuse ISM.