Selecting ads by exact keyword match
The user's search query might match multiple keywords in an advertiser's campaign that can trigger ad displays. The keyword selected determines the ad that appears in search results and its bid. When there are multiple keywords available, the system will select the one that best matches the meaning of the query.
Say for example, the user queries trips to mars in april cheap. The campaign has multiple matching keywords: trips, trips to mars, and trips to mars cheap. The algorithm will select the keyword with the closest meaning: trips to mars cheap rather than a different keyword with a higher bid. The advertiser doesn't need to adjust the selection or add any negative keywords.
For the exact keyword match, ads are selected at the group level. It means that, within an ad group, the keyword selected determines the bid that the group enters the auction with. However, ads of different groups may compete against each other in the auction. The ad that proves most effective wins.
Settings for a campaign
At the campaign level, if multiple ads from different groups have matching keywords, then, by default, ads are selected for display based on the performance indicators: CTR, quality coefficient, and bid per click. You can change this setting and select the ad with the most relevant keyword. To do this, in the advanced campaign settings under Selecting an ad for display, select By match accuracy.
We recommend that you use this setting when there is a clear distinction between ad groups in terms of keyword subjects and ad texts, and you can clearly see which query a given ad should be shown for. If you used negative keywords to differentiate impressions between your groups, with this setting you don't need to add negative keywords from neighboring groups to the given ad group.
Let's say you have two ad groups: the first group contains general ads for tiles that have keywords (roof tiles, roof covering) with high bids, and the second group is also about tiles, but ads have more specific keywords (flexible tiles, flexible tiles for home) with lower bids.
In response to the flexible tiles for home search query, with the default settings, a keyword with a higher bid from the first ad group will be selected. If you enable selection by exact keyword match, the ad from the second group is displayed, because the keyword specified for this ad more exactly matches the user query.
Since the system looks at the relevance between keywords and queries, sometimes a keyword with a closer meaning matches the query better than a keyword consisting of the same words.
For the query buy galaxy s20 128GB mobile phone, the keyword buy Samsung galaxy s20 128 gb smartphone from ad group A better matches the query (by meaning rather than words, that's why ads will be served for it). In this case, the user will see a more relevant ad for their query. For you, as an advertiser, click probability for such an ad would be higher.