Correlation between the (left) 4428 Å DIB, (middle) 5780 Å DIB and (right) 6614 Å DIB on the one hand, and the Na i D line on the other. The Galactic component (D₂ transition) is plotted with open magenta triangles and the LMC component (D₁ transition, multiplied by the ratio of intrinsic strengths of the D₂ and D₁ transition) with open cyan squares; the best fits (with rms  <1%) for both DIBs are highlighted in solid red triangles and solid blue squares for the Galactic and LMC components, respectively. Linear regression lines are overplotted, and annotated with the linear correlation coefficient.