In recent years, Melton, Wyndham and Casey, part of the Melbourne statistical division, have recorded the highest growth rate of all local government areas in Australia. Melbourne could overtake Sydney in population by 2028, The ABS has projected in two scenarios that Sydney will remain larger than Melbourne beyond 2056, albeit by a margin of less than 3% compared to a margin of 12% today. Melbourne's population could overtake that of Sydney by 2037 or 2039, according to the first scenario projected by the ABS; primarily due to larger levels of internal migration losses assumed for Sydney. Another study claims that Melbourne will surpass Sydney in population by 2040.

Melbourne's population could overtake that of Sydney by 2037 or 2039 primarily due to what factor?