Like anything that's large and involved, big science is not easy to measure. For our rankings, we took into account four objective factors: the construction costs above all, but also the operating budget, the size of the staff and the physical size of the project itself. Even these were hard to compare on an apples-to-apples basis, though, so we also used a tiering system. Then we added in three subjective factors, weighing them more heavily to reflect their relative importance: the project's scientific utility, its utility to the average person ("what will it do for me") and the always essential "wow" factor. For a complete explanation of our scoring, click here.