Estimated quasar duty cycle as a function of redshift. The blue symbols represent the duty cycles estimated with a sample of quasars mostly with M_UV < −25. The red symbols show those for the less-luminous quasars with M_UV > −25. Stars, triangles, filled circles and squares represent the results from Adelberger and Steidel (2005), Shen et al. (2007), Eftekharzadeh et al. (2015), and this work. The pink open square shows the duty cycle with the contamination correction. (Color online)