amendment to the Constitution requires approval at a referendum, by the process set out in section 128 of the Constitution. A double majority – a majority of electors and of a majority of states – is required. Constitutional referendums were based on the Swiss practice. However, the Swiss use of the popular initiative in constitutional amendment was not followed, so that constitutional alterations, although they must be approved by the people, can only be initiated by Parliament. The use of the referendum in initially adopting the Constitution, and its requirement for constitutional amendment, has been cited by justices of the High Court to argue that the Constitution is fundamentally based on popular sovereignty (rather than on the supremacy of the British Parliament, which is its technical legal foundation). This doctrine has achieved greater prominence since the cessation, in 1986, of all authority of that Parliament over Australia: see Constitutional history of Australia for details. There have been 44 proposals for constitutional amendment put to the people since Federation. Of these, only 8 have passed. The growth of central power Probably the most obvious development in Australian constitutional law has been the steady growth in the power of the federal government relative to the states. Several factors could account for this, including: doctrines of constitutional interpretation which favour a broad reading of Commonwealth powers the "fiscal imbalance" between the Commonwealth and the States (see Constitutional basis of taxation in Australia) the development of new areas of competence which did not exist at Federation, and which have fallen to the Commonwealth the growing importance of legislative areas that were always Commonwealth powers (for example, external affairs and trading corporations) constitutional amendment or referral by the States the willingness of Australian governments, including supporters of States' rights, to exercise their powers to the full Centralising interpretations Reserved State powers doctrine and the Engineers case Prior to 1920 the "reserved State powers" doctrine and "implied inter-governmental immunities" were used to preserve state power. Reserved state powers holds that the Constitution should be read in a restrictive way so as to preserve as much autonomy as possible for the States. Implied intergovernmental immunities holds that Commonwealth and States are immune to each other's laws and cannot mutually regulate each other's governmental apparatus. In 1920, the Engineer's case (after changes in the composition of the Court) swept away this doctrine. The court now insisted on adhering