Google Trends: Understanding the data.

Google Trends analyses a sample of Google web searches to determine how many searches were done over a certain period of time.

For example, if you’re doing a story about the Zika virus and you want to see if there was a recent uptick in searches on the topic, select Past 90 days. Trends analyses a sample of all searches for Zika virus within those parameters.

When you search for a term on Trends, you’ll see a graph showing the term’s popularity over time in (nearly) real time. Hovering your mouse over the graph reveals a number, which reflects how many searches have been done for the particular term relative to the total number of searches done on Google.

Numbers on the graph don't represent absolute search volume numbers, because the data is normalised and presented on a scale from 0-100, where each point on the graph is divided by the highest point, or 100. The numbers next to the search terms at the top of the graph are sums, or totals.

A line trending downward means that a search term's relative popularity is decreasing—not necessarily that the total number of searches for that term is decreasing, but that its popularity compared to other searches is shrinking.

At the bottom of your results page, the Related queries chart can show you the Top and Rising terms associated with any topic or trending story. 

The Rising tab represents terms that were searched for with the term you entered and had the most significant growth in volume over the selected time period. You’ll see a percentage of the Rising term’s growth compared to the previous time period. If you see “Breakout” instead of a percentage, it means that the search term grew by more than 5000%.

The percentages are based on the percent increase in search interest for the selected time frame. If you’re looking at the last 7 days, the benchmark for the rise in searches  would be 7 days prior; if it was the last 30 days, the benchmark would be for the 30 days prior. The only exception is when viewing the full history (2004-Present), when the percentages are benchmarked at 2004.

Trends excludes certain data from your searches:

• Searches made by very few people: Trends only analyses data for popular terms, so search terms with low volume appear as 0 for a given time period.

• Duplicate searches: Trends eliminates repeated searches from the same user over a short period of time for better overall accuracy.

• Special characters: Trends filters out queries with apostrophes and other special characters.