Left: Variability in the first moment λ₀(t) and second moment σ(t) of the double-peaked broad Hα in NGC 1097. The solid blue circles plus error bars show the measured results for the 12 high -quality spectra after the host galaxies were removed and the narrow emission lines were masked out. The solid and dashed red lines show the best descriptions and the corresponding 1RMS scatter for λ₀(t) and σ(t) determined by the maximum likelihood method combined with the MCMC technique. Right: Periodicity distributions of T_λ0 in λ₀(t) and T_σ in σ(t).