Looks like you are right. From the FAQ: >What does the y-axis mean exactly? The y-axis represents the frequency of each phrase, as a percentage of all phrases

Looks like you are right. From the FAQ: >What does the y-axis mean exactly? The y-axis represents the frequency of each phrase, as a percentage of all phrases that contain the same number of words. For example, if you search for from New York, the graph shows the number of times those words appear in exact order, divided by the total number of 3 word phrases in all of the articles I think doing it at a per-article level makes more sense for an analysis like this, but 0.02% is actually pretty significant when n is on the order of millions. Thanks for the clarification.