Power-law exponent β vs. E( B − V) (top panel) and R( V) (bottom panel) for the "β-variable" fits from Table 3. The dotted horizontal lines show the value β = 1.84. The filled triangle in the lower panel represents the sight line to the star ρ Oph from Martin & Whittet (1990). The 1σ error bars are based on fits to the Monte Carlo simulations of the data and the noise model.