The Wikipedia article on the Milky Way states that it has an estimated 100 to 400 billion stars. The one on the Andromeda states that it has about a trillion stars. With this, we can conclude that the Andromeda has between 2 and 10 times the number of stars than the Milky way.
But then there are articles like this that state that its about the same mass as the Milky Way.
The only way for both of these facts to be correct is that the stars in Andromeda are somehow lighter than the ones in the Milky way. But there is no good reason to expect this I can think of, especially over the kinds of massive numbers of stars we're talking about. If the process of star formation is equivalent, it should produce a similar distribution of stars in the two places and also the same average mass.
So, is this simply because the estimates in the Wikipedia articles are outdated? If so, what are the latest numbers?