Tidal index plotted as a function of: (upper panel) the fraction of stars formed in the past 0–1 Gyr (f_1G), 1–4 Gyr (f_4G) and 4–14 Gyr (f_14G); (lower panel) the ratio of SFR to the lifetime average SFR over the last 100 Myr (b₁₀₀), 500 Myr (b₅₀₀) and 1 Gyr (b_1G). The black open circles represent the CenA subgroup late-type dwarfs, the black filled circles are M 83 subgroup members, red triangles indicate Local Group late-type dwarf members and blue squares the M 81 group late-type dwarfs. Holmberg IX is a candidate tidal dwarf in the M 81 subgroup, and we mark it with an additional larger, open blue circle since this object is not a typical dwarf galaxy (see text for details).