Observed and modeled N_Hα/N_blue for different IMFs. The black curve show values predicted by our steep models with different IMF slopes (α). These were obtained as N_Hα/N_blue = t_Hα/t_blue while assuming instantaneous cluster formation and a constant cluster formation rate. The values predicted by the truncated models are not shown for clarity, but they are very close to the values predicted by the steep models. The first dot from the left is given by the model with the standard Salpeter IMF (α = 2.35). The red curve indicates the observed value in the M 83 outer disk using different mass selection criteria imposed by IMFs with different α. The blue curve is the same as the red curve but for the truncated IMFs with different M_u. The shaded areas around the lines show the errors in the observed values. The observations and models agree for 2.8 ≤ α ≤ 2.9, or M_u ≈ 30 M_⊙.