Introduction to Google Trends (Part One)
July 21st, 2008 at 11:38 am | by Michael Giuffrida |Google Trends is, as the logo suggests, still a part of Google Labs, making it a sister tool to Google Suggest, Google Mars and Google Sets. With Google Trends, you can track the popularity of search terms, or keywords, over time. I used this tool last month to try correlating Google Trends results with the US primaries, which generated a lot of response — much of it quite negative. My approach was just a quick look to satisfy my curiosity, and admittedly had little in the way of statistical verification — perhaps I should have waited for Google to provide better data before releasing my findings. (Google did, however, soon debut the Google 2008 US Election Trends, so they agree that Google Trends results might be at least somewhat interesting in general.)
Before getting into a detailed explanation of Google Trends, I’ll show you the graph of searches for the search term facebook, an example we’ll be using throughout this article:
Google Trends: Keyword facebook, All Regions, All Years
This chart, like all on Google Trends for Searches, includes two parts: Search Volume Index and News Reference Volume. The top one displays search volume, and that’s the one we’ll focus on here. In a nutshell, the search volume graph shows the popularity of Google searches for the term facebook over time. Those flags, A-F, give various news headlines that may have contributed to spikes in the news volume graph.
Relative Data
The main problem lies in defining the “popularity” of a search term. According to the About page, all data from Google Trends are normalized. They’re unclear about exactly how they do that, but basically, the data is all relative. The chart above shows the relative popularity of the term facebook, not just the number of searches in which the term is used. So if the popularity of the search for facebook increases, the graph is going to go up. Now, if people stop searching for other terms like myspace and linkedin, then the total number of Google searches is going to decrease and the graph for facebook is going to increase, even if the number of searches for that particular keyword don’t change, because it’s relatively more popular; it’s takes up a higher percentage of all Google searches.
Relative Scale
The scale is also a bit funky. First of all, there is no scale — none that you can see here. If you sign in with your Google account, you can then see some numbers along that y-axis, a feature Google just added.
Google Trends: Keyword facebook, All Regions, All Years
Again, we must refer to the About page to understand the scale. On all the graphs Google Trends produces, the scale is relative. Specifically, it’s relative to the average value for the time period, and that average value is set to 1. In other words, Google Trends takes all the data you see, calls the average height “1″ and then adds a fitting scale to the graph.
Here, for example, the time ranges from 2004 to the present. First, Google scales the data so that the average Search Volume Index from 2004 to the present equals 1.00. Then it simply draws lines at 2.00, 4.00 and 6.00.
Right at the start of 2008, the Search Volume Index was almost 4 times the average SVI for all time. The current value is just above 6.00, so the SVI for facebook has doubled since October 2007, when it was about 3.00. This doesn’t mean that search traffic has doubled, remember; this means that relative search traffic has doubled. In loose language, the term “facebook” takes up about twice the percentage of all Google searches that it had in October 2007. (That’s pretty good for nine months.)
That’s about it for the math behind the data. We’ll get into different techniques for manipulating the data later on, including exporting data and investigating fixed scaling. There are a few other features I want to introduce you to first.
Drilling Down: Regions
Go ahead and play with Google Trends yourself, if you haven’t yet (how could you resist?). At the top-right is a dropdown box for regions. The graphs I’ve shown you have all been worldwide; take a look at the United States-only graph.
Google Trends: Keyword facebook, United States, All Years
The first thing you’ll notice is that search traffic has been increasing much more steadily in the United States. Again, the Search Volume Index is a relative number; relative to all Google searches in the US, searches for facebook have approximately doubled over the past year.
We can also drill down by sub-regions — in the United States, we like to call our sub-regions, well, states. Check out the graph of searches made in West Virginia.
Google Trends: Keyword facebook, United States/West Virginia, All Years
Those random dips to 0 in 2007? That’s just where Google Trends didn’t have enough sample data to report a Search Volume Index. They only report numbers once they cross a certain threshold; says Google, “As an additional measure [to protect privacy], Trends only returns results for terms that receive a significant amount of search traffic.” And Google Trends only includes a sample of their actual searches anyway.
Looking at other regions can help show how Facebook’s popularity has increased, at least among those who search for it in Google. Its SVI has exploded much more recently in the United Kingdom than it did in the US. In the Mexico graph, notice that the scale goes up to 10.00; the relative popularity of the term facebook has seriously increased. In fact it seems to be about 5 times more popular than it was a year ago. Facebook added the Spanish language in February of 2008, where you can definitely see facebook gaining momentum.
Why does it drop, though, at the end of 2007? Many non-seasonal terms tend to do this. Remember that the Search Volume Index is a relative index. When Christmas rolls around, a lot of search terms spike, so even if other keywords get the same number of searches they always get, they’ll drop down lower relatively. Just look at Trends results for gift ideas, digital camera and ipod, to name a few examples.
Drilling Down: Time
Yes, there’s also the option to choose your timeframe. Google doesn’t let you specify your own start and stop dates yet, but you can choose to see Search Volume-Index over a specific year (2007, 2008, etc.), over a specific month (Jan. 2007, Feb. 2008, etc.), over the past 30 days (month-to-date), over the past year (year-to-date) or for all time (which starts in 2004), all from the same dropdown box.
Looking at a graph from the year 2007 scales so that the average Search Volume Index equals 1.00 for that year. This means that you can’t just place the 2007 and 2008 graphs side by side and compare them; the Search Volume Indices themselves will have different meanings.
What you can say, if you notice that the SVI equals 2.00 at a certain point in a graph from 2007, is that at that time the relative Google search traffic was twice the average for that year.
Regions, Cities, and Languages, and Comparing Terms
This post is intended as the first part of a three-part series. Next time I’m going to briefly explain the Regions, Cities and Languages bar graphs that appear below the main chart, and then walk you through comparing multiple search terms, which adds a whole new layer to the information Google Trends provides. In Part Three I’ll go into exporting the actual data, which, until Google releases an API for Trends, is good enough for now.
I hope this post has been informative. Most of the information here is also available on Google Trends’ About page, but this stuff is going to be essential to properly interpreting the conclusions we’ll make later on about trends.
Tags: google, google trends, normalizing, regions, scaling, search volume, time, tool