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After a week of manifesto launches, it feels like a good time to look at the track record of new governments implementing their pre-election pledges.

It's not an easy task as little research has been done in this area, but work by Dr Judith Bara at Queen Mary University of London gives us .

The first thing she found is that there has been a huge increase in the overall number of pledges made in party manifestos.

In 1945, Labour made 18 pledges in its manifesto. Ahead of the party's win in 2001, that number was 207. In separate research, the Constitution Unit at University College London counted approximately 550 Conservative pledges in 2010.

Dr Bara then looked at the nature of individual manifesto pledges, ranking them as vague, general, specific or detailed.

Focusing on the "specific" category, the pledges were compared with the new government's agenda. She found that between 1987 and 2005, 88% of these pledges were fulfilled. But over that period, only about 16% of pledges made were specific.

This may be surprising for the sceptics, but it's worth noting a couple of points.

One is that the focus is on "specific" pledges. It's difficult to say decisively whether a "vague" or "general" pledge has been implemented, so the researchers didn't include them. But importantly, the proportion of "vague" or "general" pledges was found to be increasing.

The other point is that Dr Bara's research relates to majority governments, so the winning parties have had a much easier time pushing their agendas.

When you have to govern with another party it is much more difficult. The Liberal Democrats have been saying that 75% of their 2010 manifesto made it into the coalition agreement. The UCL Constitution Unit worked this figure out.

But we're not as interested in what ended up in the coalition agreement as much as what was actually implemented - and that research has not yet been carried out.

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