Absolute top impression share (ASTS) is a metric that measures the percentage of impressions that your ads received in the absolute top position (that is the first position above the organic search results) out of the total number of impressions that were available for your ads to be shown for a specific set of keywords, during a specific time period. This metric is used to measure how often your ads are shown in the most favorable position in the search engine results page, usually called the “top position”. It’s a way to measure the competitiveness of your ads and how effectively they are competing for the valuable top spots.
A higher Absolute Top Impression Share indicates that your ads are more frequently shown in the top position and therefore reaching more people. A low Absolute Top Impression Share may indicate that your keywords and targeting settings need to be reviewed and optimized to increase the visibility of your ads in the top position.
It’s important to note that Absolute Search Impression Share is different from the Search Impression Share (SIS) which is a metric that measures the percentage of impressions that your ads received out of the total estimated number of impressions that your ad could have received, based on your current ad rank and competition.