Figure 13. The progress of fitting in one example.

The likelihood (vertical axis) that corresponds with the values of α₂ and β₂ that are reached at various stages during the fitting process - notice the final crawl along a diagonal ridge near the maximum. Along the ridge, the values of α₂ and β₂ change roughly in parallel (so the efficacy, E₂=β₂/α₂, does not change much), and the likelihood increases only slowly.