What key performance indicator (KPI) most directly indicates the efficiency of negative keywords in a Sponsored Products campaign on Amazon.co.jp?

The key performance indicator (KPI) that most directly indicates the efficiency of negative keywords in a Sponsored Products campaign on Amazon.co.jp is the reduction in irrelevant impressions and clicks, leading to an improved Advertising Cost of Sales (ACoS). Negative keywords prevent ads from showing to customers searching for terms that are not relevant to the product, thereby avoiding wasted ad spend. The most direct way to measure the efficiency is to monitor the campaign's ACoS (Advertising Cost of Sales). A lower ACoS means you're spending less on advertising for each sale you make, which directly relates to the effectiveness of your negative keywords in preventing irrelevant clicks. An increase in conversion rate is another indicator that your negative keywords are helping to filter out unqualified traffic. By eliminating irrelevant searches, you are ensuring that your ads are shown to customers who are more likely to make a purchase. For example, if you sell running shoes and add 'sandals' as a negative keyword, you will reduce impressions from customers searching for sandals, improving your ACoS by focusing your ad spend on customers looking for running shoes. The initial metric is the number of wasted impressions (and clicks) before adding negative keywords, followed by a reduced ACoS, meaning you are spending your budget more efficiently.