Google Trends allows you to look at changes over time in the popularity of different search terms, and to find search terms whose popularity is correlated. Which is a great lesson in spurious correlation. For instance, the search term most correlated with “darwin” is…”satellites”! Graph here (r=0.89). Other terms whose popularity tightly correlates with that of “darwin” include “african history”, “composers”, and “pulleys”.
The reason for the spurious correlations is obvious–so many people search Google so often on so many terms that any term is bound to be tightly correlated with some other unrelated terms. But even if you know that, it’s really hard to look at a graph like the one linked to above and not see it as suggesting some sort of causal connection. I could totally see Google Trends being a great teaching tool for undergrad stats classes.
UPDATE: Turns out that searches on “niche” are tightly correlated with (among other things) searches on “important”! Clearly not a spurious correlation! Searches on “niche” also have strong seasonality, peaking in April and October, and plummeting around Christmas and in June and July. I guess that’s because most searches on “niche” come from undergraduate ecology students who’ve just been taught the concept in their classes.
I really need to stop playing with Google Trends and get to work…