Top panel: number of active dwarfs as a function of spectral type. Bottom panel: activity strength as a function of spectral type for DR7 (M0–M6), BUD (M7–M9), and the L dwarf activity sample (L0–L5; including the BUD L dwarfs; discussed in Section 5.2). The minimum and maximum (light gray bars), the interquartile range (dark gray bars), and median values (black circles) are shown. The upper envelope of the M0–M6 spectral type bins is likely affected by the serendipitous detection of Hα emission during flares, an effect that is most noticeable for M2–M4 dwarfs where strong flares are common. In these bins, the strongest detections overestimate the Hα range observed in quiescence. The dashed red line shows the effective lower limit of detection for SDSS data (based on the 0.75 Å Hα EW threshold; one L2 dwarf from the non-SDSS portion of the L activity sample falls below the limit). The Mohanty et al. (2002) threshold is also shown (vertical purple dashed line), see Section 7.3.