Upper panel: comparison of Q_pair vs. Q_LSS, isolated pairs (green stars), SDSS single galaxies (magenta circles), and SDSS pairs (blue pluses). For isolated galaxies (red triangles) there is not Q_pair available, but we consider Q_pair = Q_LSS for comparison purposes. The black dashed line represents the line where Q_pair = Q_LSS. Lower panel: schema of the sample definition, total number of galaxies (N_T) in each sample and number of galaxies in common (N_C), and environment definition for the SIG and SIP samples (red and green circles, respectively), and for control samples (blue and magenta ellipses for SDSS pairs and SDSS singles, respectively). The arrows in the axis indicate the direction to higher values of the tidal strength.