Arthur Sale, professor of computing at the University of Tasmania, has carried out a study on different Australian universities. All have Open Access repositories but differ in their Open Access policy implementation.
When the study was carried out, the University of Tasmania had no policy on Open Access and no advocacy campaign (it has since changed these conditions). The graph below shows the outcome. The blue line represents the number of articles published from the University of Tasmania resulting from research supported by the Australian Government, that is, publicly-funded research. At the time of the study, the department that funded research was called the Department of Education, Skills and Training (DEST). The white line shows the number of articles in the university repository. Only a small proportion of publicly-funded research was self-archived in the repository over the time of the study.

The University of Queensland does not have a policy on Open Access but it had a very active advocacy and education activity carried out by the library. This ensured that researchers were well-informed about the repository and its purpose. The graph below shows the self-archiving pattern for this repository. The slope of the blue line is better than for Tasmania and a greater proportion of publicly-funded research is being made Open Access, but still only a minor proportion of the whole.
This university has a mandatory Open Access policy. The graph not only shows that this policy has resulted in a high level of self-archiving by researchers but it also shows the point where this changed, from the usual low level seen where there is no mandate, to the high level that results when a policy is mandatory. The point at which the rate of self-archiving began to rise is soon after the mandate was introduced in 2004.

A downloadable version of this summary of the Sale study is here.
Original study: Sale, AHJ (2006) Comparison of IR content policies in Australia. First Monday, 11 (4).