Based on advertiser requests, we will soon offer ad group level impression share metrics for the Search and Display Networks. Once released, you can use ad group impression share data to, for example, better identify high performing ad groups that aren't capturing the majority of available impressions.
In the next few weeks, you will see three new columns that can be added to your ad groups tab: 1.Impr. Share: the percentage of impressions you received divided by the estimated number of impressions you were eligible to receive. 2.Lost IS (Rank): the share of impressions lost due to your Ad Rank. Note that Lost IS (rank) will not be shown if you were at or near your budget for part or all of a given day (a.k.a. were “budget constrained”) during the date range being examined. 3.Exact Match IS: (Search Network only) the percentage of impressions you received for searches that exactly matched your keyword divided by the estimated number of exact match impressions you were eligible to receive.
In addition to providing more detailed metrics, we are also planning to update our algorithms to provide more accurate campaign impression share metrics.