When Google launched its "Search, plus Your World" (SPYW) feature back in January, there were some concerns that the service, by prioritizing Google+ search results, would have a negative impact on SEO traffic to competing social networks. Now, a report from analytics company PageLever shows that traffic from Google to Facebook fan pages has indeed dropped in the five months since SPYW went into effect, though these results are far from conclusive.

PageLever's study centered around a sample of 500 Facebook fan pages (each with a minimum of 100,000 fans), focusing on external referrals from both Bing and Google. Between April of last year and January 9th — a day before SPYW went into effect — each page in this sample averaged about 9.25 referrals from Google per day. From January 10th to April 15th, however, this average plummeted to just 4.52 external referrals per day — a drop of about 51 percent. Interestingly enough, traffic began dropping off about three days before SPYW launched, suggesting, perhaps, that Google changed its algorithm a few days in advance.

At first glance, then, it would appear that SPYW did indeed have a detrimental effect on Facebook's search engine traffic. Complicating this hypothesis, though, is the fact that traffic from Bing also declined over this same time span, and by an even greater margin — about 61 percent between pre- and post-SPYW eras.

This drop in Bing-generated traffic makes it even harder to isolate SPYW's impact, though there are some important caveats to consider. For one, PageLever's report didn't account for internal referral traffic — i.e., traffic resulting from searches within Facebook. This omission could prove rather significant, since these data could, for example, determine whether declines in external referrals are offset by gains in internal search traffic.

Also of note is the fact that between August 2010 and March 2011, PageLever's sample of Facebook pages averaged about 6.3 Google referrals per day, per page — higher than the referrals seen since SPYW went into effect, but about 32 percent lower than the traffic seen between April 2011 and January 2012 (PageLever says it found no signs of seasonal trends in its dataset). In other words, Facebook's search traffic may have declined within the past few months, but this drop doesn't seem quite as severe when taken within a larger context.