(Update on 2008-07-10: It appears, with the latest update to Google Trends, the “bug” I describe below has been fixed)
In case you’re not familiar with Google Trends, it allows you to graph the popularity of the search terms that people enter into Google Search. You can graph up to five terms, separated by commas, and it will chart the relative popularity of the terms over time, as far back as 2004. I believe Google Trends has been available for well over a year, although it has recently (as of Oct. 2007) been improved so that statistics are now updated every 24 hours. The one problem I’ve encountered is with search terms that are too specific or unpopular. For such terms, instead of producing a chart, it just complains: “Your terms … do not have enough search volume to show graphs”. I suspect Google Trends initially checks *only* the first term against its database or some threshold of search volume. If that first term isn’t popular enough, it returns the “not enough search volume” error message. So you should put what you believe to be the most popular term first. This way, you are more likely to get results. For example, try two popular stock ticker symbols: GOOG and MSFT - plus an “unpopular”, fictitious symbol: ZYXW. If I enter ZYXW, GOOG, MSFT, Google Trends claims (as of the date I write this) it can’t produce a chart. But if I move “ZYXW” to the middle term (GOOG, ZYXW, MSFT), Google Trends happily creates a chart this time, just with no sign of the unpopular “ZYXW”. This seems like a bug to me (or arguably a design decision). I couldn’t find any complaints related to this in the Google Trends Forum so, either most people enter terms which are more popular than mine, so they rarely get the “not enough search volume” error or they just aren’t bothered by it enough to complain in the forum.
(Update on 2008-05-30: I had to replace my original dummy “stock symbol”, FOOG, with ZYXW instead. ‘FOOG’, which was just a mutation of ‘GOOG’ that I made up, now has 145,000 hits in Google search and so is now ‘popular’ enough for Google Trends and broke my example.)