Why is an even-odd split 'faster' for MergeSort? MergeSort is a divide-and-conquer algorithm that divides the input into several parts and solves the parts recursively.
...There are several approaches for the split function. One way is to split down the middle. That approach has some nice properties, however, we'll focus on a method that's a little bit faster: even-odd split. The idea is to put every even-position element in one list, and every odd-position in another.

This is straight from my lecture notes. Why exactly is it the case that the even-odd split is faster than down the middle of the array?
I'm speculating it has something to do with the list being passed into MergeSort and having the quality of already sorted, but I'm not entirely sure.
Could anyone shed some light on this?
Looking at the graphing network on Wikipedia and this page for even-odd merge sort it appears that it has a higher complexity than traditional merge-sort. However, at the cost of more operations, notice how the operations remain independent of one another.

That is to say, where as in merge sort you eventually end up merging 4 lists and then 2 lists, which cannot be done in parallel, even-odd merge sort allows you to operate in parallel until the end of the algorithm.

The Wikipedia article also points out that it is reasonably fast for doing sort in graphics hardware. I suspect this is because where as merge sort your inputs to compare-and-swap depend on which previous element was merged, the inputs to compare-and-swap in even-odd-merge-sort are always the same.

Hope that helps!