Fraction of active M and L dwarfs (as determined by the presence of Hα emission with an EW > 0.75 Å) as a function of spectral type. Fractions computed from the W11 sample (red), from the BUD sample (black), and from the L dwarf activity sample (described in Section 5.2; blue) are shown with uncertainties based on a binomial distribution. For the spectral type bins with no detections, the arrows show upper limits also based on a binomial distribution. The total number of objects used to compute the fraction (active and inactive) are shown above or below the data in corresponding colors. The Mohanty et al. (2002) threshold is shown (vertical purple dotted line) between M9 and L0, corresponding to ﹩{{T}_{{\rm eff}}}﹩ = 2300 K (as discussed in Section 7.3).