these are the few points which i have got for your question if you want more information you can check out with this url : searchmarketing.yahoo.com/re/srch/cipref.php

You may find that some or all of your Click Index meters are blank. This doesn't mean that your Click Index score is 0; rather, it simply indicates that the listing hasn't received enough impressions to calculate a score. Listings that are in danger of removal will show a score of 1 bar.

You can have a click-through rate on a given listing that is relatively high compared to your other listings, while still having a low Click Index score. This is because Click Index scores are calculated by comparing the click-through rate on your listing to other listings that are displayed for that same search term. No comparison is made to your other listings for different search terms.