Correlation of the fraction of [C II] emission from the ionized gas with: metallicity, specific star-formation rate, and line ratios for which the strongest trends are found. Values for the y-axis are taken from the models in boldface in Tables 3 and 4 (triangles for single models, filled circles for mixed models). Color coding corresponds to metallicity, except for the last two panels which are color coded by electron density and ionization parameter (of component #2 in case of mixed models). Spearman’s rank correlation coefficient and significance of its deviation from zero in parenthesis are indicated in the top-right corner (ρ). In the last three panels, star symbols are the ratios of observed [C II]₁₅₇ or [O III]₈₈ intensity divided by the predicted [N II]₁₂₂ intensity. The correlation coefficients ρ_all include those star symbols.