How does keyword stemming in Japanese affect the precision of 'exact match' keyword targeting compared to English?

Keyword stemming, the process of reducing words to their root form, has a different effect on the precision of 'exact match' keyword targeting in Japanese compared to English primarily because of fundamental differences in language morphology. In English, stemming often involves removing suffixes (like '-ing', '-ed', '-s') to match variations of a word (e.g., 'running' stemmed to 'run'). 'Exact match' in English still usually accounts for minor variations like pluralization or misspellings close to the target keyword. However, Japanese is an agglutinative language, meaning words are formed by stringing together multiple morphemes (meaningful units), including prefixes, suffixes, and particles, which dramatically alter a word's meaning or grammatical function. Japanese also doesn't have spaces between words, making word boundary detection harder. Due to the agglutinative nature, stemming in Japanese can be very aggressive, potentially matching ads to search queries that have a related root but a completely different intended meaning due to added morphemes. For example, if the exact match keyword is '食べます' (tabemasu - 'to eat' polite form), aggressive stemming might match queries containing only '食べ' (tabe - the root 'eat'), even if followed by other characters making it a different verb or noun altogether. This reduces the precision of exact match. Furthermore, honorifics (keigo) add complexity. Stemming '行きます' (ikimasu - 'to go' polite form) could lead to matches with less polite or even rude variations of the same verb, which is undesirable. This difference means 'exact match' in Japanese is less precise than in English because stemming can inadvertently broaden the scope, leading to unintended and potentially irrelevant ad impressions. Therefore, managing negative keywords becomes more critical to refine targeting in Japanese campaigns.