The cause of one of the most important changes in Australian household financial behaviour in recent times - the rise in savings levels - is not clear, according to Reserve Bank research.The RBA has published a research paper written by two members of the bank's economic analysis department, which looks at the steady decline in the household savings rate from the early 1970s to the mid 2000s and the reversal of that trend in the second half of the 2000s.The researchers said that it was important to understand the reasons for the change because the extent to which the higher savings ratio will be sustained depends on what caused the change in behaviour.Australia's household savings ratio fell from around 20 per cent of disposable income in the early 1970s to around zero by the early 2000s. Things turned around in the second half of the 2000s and the current savings ratio is about 10 per cent.As a general rule, saving increases with higher income, while it falls with higher wealth. Financially constrained and migrant households tend to save more than other households.Factors contributing to the reduction in the savings rate from the 1970s included the increased availability of credit, falling real interest rates, greater economic stability, rising asset prices, rising household income and income expectations, and high household confidence.In the mid 2000s households with less secure income and those vulnerable to asset price shocks, higher-educated households, younger households with debt and older households with wealth all tended to increase their savings.Factors contributing to increased saving included a reduction in future income expectations, an effort to rebuild wealth after the financial crisis, changing attitudes to debt and changing consumption patterns. However, the researchers did not come to any final conclusion and left open the possibility of other interpretations. "We are unable to definitively conclude what caused this change in behaviour," they said.