"Marketers should define the value of a fan based on how it impacts the key criteria that determines the success or failure of their business," says Kalehoff. Specifically, marketers should measure the spending habits of fans versus non-fans, to see if fans are more likely to make a purchase, make purchases at great amounts and/or purchase repeatedly. Advocacy — the probability of a customer recommending a product to others, and the probability of that recommendation to affect sales — is another key metric. Another area that is more difficult to measure is brand affinity — that is, the emotional draw that a customer feels towards a brand because of the relationship that develops between brands and fans over Facebook. If positive brand affinity tends to be a powerful sales indicator on other channels, it may be worth cultivating on Facebook, too.