What is the difference between impression share and search impression share and why is this important for campaign optimization on Yahoo! Japan?

Impression share and search impression share are distinct metrics that indicate how often your ads are showing relative to the total available opportunities on Yahoo! Japan, and understanding their difference is crucial for effective campaign optimization. Impression share (IS) measures the percentage of times your ads were shown out of the total number of times they *could have been shownfor all eligible searches and placements within your targeting settings. This includes display network and other placements beyond just search results. Search impression share (SIS), a subset of impression share, specifically measures the percentage of times your ads were shown out of the total number of times they *could have been shownon the Yahoo! Japan search results page for queries that matched your keywords. The difference lies in the scope: impression share is broader and includes all eligible placements, while search impression share focuses solely on search results. For example, if impression share is high (e.g., 80%) but search impression share is low (e.g., 30%), this suggests your ads are showing frequently on the display network, but are missing out on many relevant search queries. This indicates you might need to increase bids, improve ad relevance, or refine keyword targeting to capture more search traffic. If SIS is low due to budget constraints, increasing budget will likely lead to more impressions. If SIS is low due to rank, then improving Quality Score or increasing bids would lead to more impressions. Monitoring both metrics allows for granular optimization, ensuring campaigns are maximizing visibility across different channels and effectively capturing valuable search traffic. Ignoring the distinction leads to an incomplete picture and suboptimal decision-making.