It's an equation for the data (for the purpose of describing the data) -- not an equation of the data. That would be an equation belonging to the data. What would that mean???
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Ant_222CJ, how would you translate an Anatoliy Dneprov's book's title — "The equation of (for) immortality". I'd go for "of"...I don't advise translating a title until you've translated the whole book.