I found that Yahoo Searchmarketing Report have a very big different with webalizer, Awstats or Google Analytics. Eg. From Yahoo Report: keyword1 is 100 clicks per month. Total amount is about $100 But web statistic is 10 - 25 clicks only. I have phone to Yahoo Search Centre. But Yahoo cannot solve the problem. They said that their system is OK. They don't know the reason.
It might appear too obvious, or maybe I'm just underestimating you (and if I am, it's not my intention): Yahoo gives you info of RAW clicks, while differrent stat-tools give you also the unique number. make sure you're looking at the same one.
Also, Yahoo's interface includes clicks from partner sites... are you checking your stats By Site (e.g. Yahooo.Com), or using a tracking ID to track the entire Yahoo account?