Is Google`s Keyword Tool Accurate? Analysis Using Actual Data
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Many SEOs wonder if Google's Keyword tool is accurate. In fact, this is a very common question in SEO. This article attempts to explore the accuracy of this tool with respect to its use in keyword research for search engine optimization.
It is important to work with accurate data when doing keyword research. There are two reasons for this. First, if you are doing SEO for client websites, particularly if you've been assigned to do keyword research using Google's Keyword tool, it is important that your search traffic predictions are similar to the actual results. Customer expectations are mostly based on traffic and conversions, so it's valuable to know the accuracy of the tool you are using.
Second, estimated sales based on conversions also use search query volume data, which can be taken from Google's Keyword tool. If the data you are gathering is highly inaccurate, then you will come up with some unrealistic estimates for sales and conversions.
Scope and limitation of this study
You need to determine first what sets of data need to be compared. Suppose you focus on global or worldwide results as opposed to local search results. In Google's Keyword tool, you can clearly see the “Global Monthly Searches” column. See screen shot:
According to Google, this is the estimated 12-month “average” of user queries in Google's search engine. Meanwhile, the “impressions” data in Google Webmaster Tools shows the exact volume of search queries done for that specific keyword, where your website is ranking in Google search results.
But note that the Google Webmaster Tools impression data is NOT a “12-month average;” it only applies to the latest/current month (e.g December 10, 2010 to January 9, 2011). You might be aware of the “trending” and “seasonal” effect on search volume queries. So you can expect some errors based on this effect.
This is one limitation of this study, since you cannot do a “one-to-one” comparison between Google's Keyword tool data and Google Webmaster Tools data using the same time frame. For example, if you intend to gather the November 2010 data from the keyword tool, you cannot get the equivalent November 2010 impression data with Google Webmaster Tools because it will display only the current/active one month set of data.
Likewise, if you use the latest impression data, you cannot get the equivalent "latest month" data with Google's Keyword tool, because the latest they can provide is the November 2010 data (if you are gathering data in January 2011). See screen shot below:
In this study, you can only compare the global monthly search volume (12-month average) to the latest one month impressions data available in Google Webmaster Tools. Another factor considered in this study is the “match types.” Google's Keyword tool offers three match types to get monthly searches data. These are the "broad," "exact" and "phrase" matches.
Some SEO practitioners often used the “exact” match type, as this appears to be closer to the exact data. But no conclusive test has been made advising that one should use either an “exact,” “phrase” or “broad” match to get more accurate estimates of actual search volume queries. This factor is considered in this study.
Google Optimization 
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