( Yamashita Tomohisa, flumpool, Tohoshinki, Itano Tomomi, YUI...Collapse )
The NINKI ratings are the results of a poll conducted by Oricon indicating interest in an upcoming release. Although the ratings are never a true reflection of sales, it does give a strong prediction about where the single/album will place in terms of popularity amongst the Japanese public. However, they are NOT an indication of how it will perform in terms of chart positioning and total sales for the week.
Oricon used to poll around 400 of its members for NINKI ratings, but since some popular artists have had NINKI exceeding 500, we can only assume that Oricon has extended the polling to around 600/700 people now.
Source 1, 2