Effect of the K-correction on photometric properties of our SN IIn sample. The required correction is smaller than ∼0.2 mag in both peak magnitudes and mag_50 d at redshifts ≲0.15, although it can be as high as 0.3 mag at z ≳ 0.3. The inset shows the effects of the K-correction on the light-curve slopes measured from peak to +50 d, which is smaller than 1.5 × 10⁻³ mag for all the redshifts of our sample.