The inner disk frequencies (f_id) in different star formation regions as a function of age. The frequencies are estimated from H − K_s vs. K −  [3.6]  and H − K_s vs. K −  [4.5]  color–color diagrams. The frequencies are estimated for stars with masses larger than 0.5 M_⊙, which is the mass completeness limit for Pismis 24 cluster. The dashed line is the fit to inner disk frequencies of the four clusters, Pismis 24, NGC 2244, NGC 6611, and γ vel, which gives f_id = e^−t/1.0, whereas the solid line is the fit to all other star formation regions, which is f_id = e^−t/2.3. Here t is the age in Myr.