Posterior distributions of v_g determined by different techniques. DECIGO data under observing strategies I (one-month) and II (one-year) are compared with two other methods: a direct method based on transit time across a separated network of detectors, and an indirect method using the time delay of GW170817. Two strategies were considered: LIGO O2 – data from O2 of Advanced LIGO-Virgo – and LIGO O2 fixed – where the sky localization of the BNS source is fixed. Note that LIGO O2 and GW170817 only provide constraints on v_g/c, and at low redshifts, we take c = c₀ in this figure.