Iffy math

Booklist recently posted an article about the massive increase in the length of middle-grade literature over the past 40 years, attributing the 173% increase to the popularity of the Harry Potter series. Unfortunately, the author doesn't seem to consider changes in font or style, which I would assume accounts for at least some of the page difference between, say, the 1978 novel The Westing Game (192 pages) and The Maze of Bones (220 pages), the first installment in the 39 Clues series. Sure, Maze is nearly 15% longer, but the typesetters have also pumped up the font size and word spacing like high school students hoping to hit their minimum page count. I definitely agree books are getting longer, but I think this kind of study might have been more accurately determined by word count.