Comment on "Isoelectronic Ru substitution at Fe-site in Sm(Fe_{1-x}Ru_x)AsO_{0.85}F_{0.15} compound and its effects on structural, superconducting and normal state properties" (arXiv:1004.1978)

Based on the five-orbital model, we derive the reduced impurity scattering rate $g=z\gamma/2\pi T_{c0}$ in Sm(Fe$_{1-x}$Ru$_{x}$)AsO$_{0.85}$F$_{0.15}$ from the residual resistivity. At $x=0$, the transition temperature is $T_{c0}=50$ K. For $0.05<x<0.36$ ($0.84>T_{c}/T_{c0}>0.3$) the obtained value of $g$ ranges from 1.5 to 2.9, which suggests that the $s_\pm$-wave state cannot survive. We point out that the magnetoresistance frequently gives an underestimated value of $g$ in correlated electron systems.