Historical rankings of Prime Ministers of Australia teaching or researching in the fields of Australian politics or history" to place Australia's prime ministers in five categories; 40 responded. Five points were awarded to prime ministers judged "outstanding", four for those considered "good", three for "average", two for "below average", and one for "failure". The three caretaker prime ministers were excluded from consideration, as was the serving prime minister, Julia Gillard. John Curtin received the highest average rating, 4.78, and he was the only prime minister who no respondents gave a rating lower than "good". It is possible to compare the highest approval ratings achieved by Prime Ministers
Acting prime minister is on vacation, or is in ill health. In the early 20th century, when travel by ship was still the norm, it was not uncommon for there to be an acting Prime Minister for months on end. The deputy Prime Minister is usually designated as the acting Prime Minister, although another senior member of the government may fill the role if both the Prime Minister and deputy Prime Minister are unavailable. An acting Prime Minister is required quite frequently – for instance, between 3 December 2007 and 23 February 2009 (during Kevin Rudd's first term), Julia Gillard acted as Prime