The Google Keyword Tool displays search data. The data may vary because of the ad group that a user has chosen, or whether the tool has been accessed from outside of his or her account.  The Competition column will give you an idea of how many advertisers are actually bidding for popular term/ phrase. This piece of information can help you decide how competitive a particular ad placement is.

Following are a few vital aspects related to potential impact of relevant keyword ideas:

1. The keyword idea engines will generate rough estimates of the potential clicks, impressions as well as cost of a particular keyword idea. The estimated numbers indicate the additional potential clicks and impressions that you probably could derive from it apart from the estimated cost. Usually, the estimates won’t include the clicks, impressions and cost from current key terms of that ad group.
2. Your campaign settings are used by potential estimates to work out as which networks to be included. If you have chosen Google search, they (the estimates) will incorporate potential clicks, impressions and cost from this particular network.
3. If you’re opted into AdSense (for search as well as Google search), the potential impact of both will be included in the estimates. They do not reflect performance on Google’s Display Network.
4. You may find that some keyword ideas are missing out on potential estimates. The ad group ought to have had some amount of activity recently on Google search (or AdSense for search) for a keyword idea to having potential estimates. Deleted or paused ad groups are ineligible since the system invariably relies on current search data for the purpose of generating estimates.
5. Although the Google Adwords strives to offer potential estimates for a wide array of keyword ideas, some of them don’t have potential estimates since the campaigns or ad groups employ AdWords features not backed by its estimation system (automated bidding, for instance).
6. If you are evaluating a host of keyword ideas, potential clicks, impressions and cost of each one are independently delivered. Keep in mind the fact that estimates for one keyword idea should not be summed with that of another while arriving at a total estimate at the overall campaign or your account level. Say for example, if two similar ideas are recommended for two diverse ad groups, they may have click, impression and cost estimates well in common. And combining potential estimates of both ideas could end up inflating the calculation.
7. Keyword ideas make use of default maximum CPC bid of the ad group in order to generate estimates. While viewing a keyword idea, a user can opt to change the bid, which is assigned to each key term.

For the Search Network, consider employing the Search Terms report to further enhance and update your keyword list. The report will inform you about the exact search queries people used to find your ad. With this piece of data you can add or remove keywords from your list.