I have an apology to make. In my January column, “Five Myths of Recycling,” I estimated a printed paper recycling rate of 72 percent. After looking at more data, I don’t think I got that number right, although I do think I’m relatively close.

So how did I go wrong? I relied on EPA data to estimate that recycling rate, as I have for years. However, for 2010, EPA changed the methodology it uses to estimate paper recycling. In previous years, the agency has given individual generation and recycling tonnages for all of the different types of printed paper such as newspapers, office paper, mail, commercial printing, etc. For 2010, however, the agency estimated how much of those individual grades was generated, but not how much was recycled.

Instead, EPA’s latest report gave an overall recovery tonnage for “nondurable paper and paperboard products. ” That larger universe includes all of the different types of printed paper along with products such as tissues, towels, plates and a “miscellaneous” category of paper used in games, novelties, cards and other products. Recycling of these additional products is so minimal that in the past EPA has always called it “negligible. ” Their recycling remains minimal today even though some programs are starting to accept a limited number of these products such as paper cups.

Given this new data set, I added up the generation tonnages and divided the total into the overall recovery tonnage for the nondurable paper and paperboard products category. That gave me a 72-percent recycling rate. Using the same methodology for 2009, when EPA listed the individual recovery tonnages for each kind of printed paper, the recycling rate is 71 percent.

So, was I wrong? Probably. The paper industry estimates a 72-percent newspaper/mechanical paper recycling rate and a 55-percent printing and writing paper recycling rate for 2010. Combining the two categories gives a 60-percent recycling rate. But the industry and EPA use different databases, so who knows what the right number is.

I felt a little better about my possible error when EPA revised some of its 2010 data in mid-February, less than 3 months after the agency released its 2010 report. While the revisions covered PET bottle and electronics recycling, the agency doesn’t normally revise numbers midyear. EPA always revises data for previous years when it releases a new yearly report, but it never says what was changed or why. Only numbers nerds like me notice the changes.

EPA’s 2010 report includes a footnote to the paper data in which it concedes it cannot assess recovery of subcategories such as office paper or commercial printing. Why? The agency doesn’t say. My guess is that because many recycling programs collect mixed paper and Chinese paper mills are willing to pay good money for it, EPA is finding it possible to estimate recycling rates for individual grades of printed paper.

Let’s face it. We don’t know exactly how much garbage we make. Even our ability to estimate recycling rates is limited. At best we have highly sophisticated guesstimates based on computer models and compilations of disposal and recycling tonnages prepared every year by the states. In an upcoming column, I’ll look at EPA and state data and see what makes sense. And if I can figure out a more accurate recycling rate for printed paper, I’ll let you know.