When I first began covering the religion category for PW in the early 1990s, it had become the fair-haired child of publishing, posting sales figures that made many in the industry shake their heads in amazement. This was especially true in the world of New York trade publishing, where religion was a topic little understood and uncomfortable for many.

Data in publishing is notoriously slippery, and that is especially true in religion, a category that crosses many genres and other categories. “What is a religion book?” is a question not always easily answered, and trying to get a clear picture of sales continues to be a challenge.

At BEA 2008, Al Greco, senior researcher of the Institute for Publishing Research, delivered more great news for the category, projecting growth of more than 5% from 2008 through 2011, nearly twice that predicted for adult trade overall. That followed a 2007 that, according to BISG, had seen gains of 6.3% in net sales and 4.2% in units sold, compared to 4.4% net sales and 0.9% in units for adult trade overall.

Even those of us who wanted to believe that rosy scenario wondered if it could hold, and this year—in the wake of the economic storm when everything changed—BISG's numbers told a very different story, showing a 10% drop for 2008 and a projected decline of 4% for 2009.

In religion, how you count is as important as what you count. BISG changed its methodology this year, bringing in a new research company, Outsell Inc., to conduct surveys and interviews with the full range of publishers, from the majors right down to single-title and self-publishers. The change accelerated a direction BISG has been moving in recently, says Leigh Watson Healy, chief analyst for Outsell. While emphasizing she is not an official spokesperson for BISG (director Michael Healy was traveling and unavailable), she says the organization began “three or four years ago to dive more deeply into data-gathering for the long tail of small to midsize publishers”—those with revenue under $50 million a year—which it felt had been “underrepresented.” That aligned BISG's “universe” of publishers with Bowker's, which began to include the smaller publishers in its data about five years ago.

Did the new methodology lead to a substantially different sample—and, to a greater extent than ever before, a self-selected one? Says Watson Healy, “Yes, the survey sample expanded, but the universe is essentially the same. What changed was bringing the top tier of larger publishers into the [self-reported] survey methodology,” adding to the data collected about them from traditional sources. The change was factored into the final product through additional interviews and “chasing down publishers we knew we needed to hear from,” she says.

Al Greco, who has long worked with BISG on data gathering, disagrees on the significance of the long tail (“these are companies who do very little business”) and is partnering with PW on a new project, the PW-IPR Book Sales Index, which uses the traditional economic data he relies on as well as the unit-sales numbers PW has gathered for years for its annual “The Red & the Black” feature (now called “Bestselling Books” and covered each March). Greco expects “a modest uptick [for religion] in 2010, and an increase in 2011 and out because of improvement in the economy. I think it will really bounce back in 2011—2012.”

The conventional wisdom always has been that bad times are good for religion and spirituality books, because people seek the comfort and guidance they offer. But just as Americans have cut way back on buying cars, eating out and other discretionary spending, they have also cut back on their book purchases, and this time religion isn't any exception. What is happening to religion book sales is what has happened to all of us—the economy.

Missing now, too, are the megabestsellers on the scale we saw in the 1990s and the early part of this decade. Early in that decade, it was The Celestine Prophecy, Embraced by the Light andConversations with God. Then, when evangelical Christian books flowed into the mainstream, came the juggernauts: The Purpose-Driven Life, Left Behind, The Prayer of Jabez—all of which ended up selling 20 million—40+-million copies and skewed sales stats for years. The copycat books have been legion, and publishers have been throwing major money at pastor-authors and novelists they hoped could duplicate those successes. Some recent books have done very well—think Joel Osteen and The Shack—but none has scaled heavenly heights.

Maybe the bloated sales of The Purpose-Driven Life et al. were like the stratospheric real estate values and Wall Street bonuses—signs of irrationally exuberant times, gone for now, may be gone for good. When it comes to pastor-authors, demographics will also come into play. Many younger Christians are drawn to small, intimate congregations (witness the proliferation of house churches) and are mistrustful of megachurches. “It's tough to imagine them embracing that kind of personality,” says Greg Daniel, a Nashville literary agent. “They also mistrust [marketing] campaigns, and that's what those books are based on.”

More and better sales data, whoever provides it, could paint a clearer picture of exactly what's happening in religion, and there's no doubt that would be helpful to publishers. Still, publishing is an unpredictable enterprise. The big books, the culture changers, come out of nowhere, unexpected and unduplicatable. Some author somewhere has to write something that strikes a mysterious chord in the souls of millions of readers. The wonderful thing about books is, that could happen anytime.