One of the arguments in favour of mixed member proportional (MMP) is that it is better for women. It is an argument that has been used during the Ontario referendum fairly frequently, so I thought I would give it some analysis.
In Canada and the United States there are far fewer women in elected office than in the population as a whole. Women make up approximately 50% of the population (actually a bit more) but only make up roughly one in five of all politicians. Studies have indicated all sorts of reasons why this is the case. Political parties have made some attempts at trying to deal directly with these problems while others have tried to make it easier for women to become candidates in order to balance out some of the problems. One means of balancing these problems would be to change the system, which many would argue is indeed one of the problems in the first place.
The evidence around the world is very clear, it is possible to increase the number of women in politics by changing our system. There are many comparators we could use but there are also many variables besides the political system in use (i.e.: culture, economy, politics, etc.).
Personally I believe that the Netherlands is a reasonable comparison. One in three of their politicians are women compared to one in five for ours. The Netherlands uses a system of multi-member districts (the proposed electoral reform voted on recently in British Columbia used a system with multi-member districts) and open lists (the proposed MMP in Ontario would be a closed list - the parties appoint candidates to the lists and voters vote for the party as opposed to the voters being able to vote for and select the candidates).
Those opposed to MMP would argue that the system is not the main problem with why women are not better represented among our elected officials. They would argue a less dramatic change without the negatives they see in MMP could be just as effective at increasing the number of women. They have also been arguing that the prospect of fringe parties such as the religious right forming the balance of power in Ontario would be detrimental for women and other groups.
In the end I think it is safe to say that the MMP system being proposed will almost certainly result in more women. However, one will need to balance the net negatives and benefits with this to determine whether MMP as proposed will be better for women. And that is an analysis that can really only be done by each individual.