People who are fans don’t spend more money because they’re on Facebook, they become fans on Facebook because they would already spend that money.

Of course it’s in Facebook’s best interest to show that people who are fans spend more money. Without that, why would companies buy ads on Facebook?

I just think we should think about why people become fans of a brand on Facebook. They already have an interest and desire to be more involved in the brand. They may be looking for deals or looking to contact other people who are interested in the brand. But they’re already a fan.

I wonder if anyone is asking what they spent on the brand before they became a fan on Facebook. That would at least give some indication as to whether or not Facebook is influencing purchasing or simply the by-product of people who are already fans.

Lots of companies — more every day, it seems — want to have Facebook “fan” pages, where customers or would-be customers can connect with them and become part of their online community. But what are those fans actually worth to a company? Everyone has their own views on that question, but now a social media measurement firm called Syncapse has come up with an actual dollar value in a report released today (PDF link). The answer? An average fan is apparently worth about $136.38, although for some very successful social marketers the value can be dramatically higher, while for some less successful companies it can be virtually zero.

Syncapse came up with the figure by asking 4,000 fans of 20 of the top brands on Facebook — including Nokia, BlackBerry, Victoria’s Secret, Adidas, Nike, Coca-Cola, Starbucks and McDonald’s — why they were fans of those companies or brands, and about their past and future purchasing behavior. Syncapse then tried to estimate what the value of each fan’s spending would be to a company, as well as the value of continuing to have that fan as a customer over time.

The key findings of the report are likely to come as music to the ears of advertisers that have been pursuing a Facebook-based social media strategy. According to the survey:

• On average, fans spend an extra $71.84 they would not otherwise spend on products they describe themselves as fans of, compared to those who are not fans.
• Fans are 28 percent more likely than non-fans to continue using a specific brand.
• Fans are 41 percent more likely than non-fans to recommend a product they are a fan of to their friends.

That probably helps to explain why, according to recent statement by the company, the number of advertisers working with Facebook has doubled in the past year. But Syncapse also said that its results showed how the value of a fan can vary widely.