Media folks are buzzing this week over a Stanford study about the nutritional differences between organic and conventional foods.

The study found almost no differences.

Those who cling to the idea that organic foods are better for your health have begun to scrutinize the study, as any critic should.

That begs the question: is the study any good?

First, you’ll need to read the article, but you will have to pay for the information. Unless you have a subscription to the Annals of Internal Medicine or access to Medline, you’ll need to go to the journal website and pay $19.95 to download the article.

Getting a bead on scientific research means a quick lesson in how the study was conducted and what the researchers use to determine whether results are significant. It also helps to know the researchers’ motivations.

In the Stanford study the researchers didn’t do their own primary research: instead they conducted a meta-analysis of existing studies.

A meta-analysis is used frequently in health research to give scientists a sense of the big picture of some phenomenon.

“Meta” is from the Greek, meaning “with” or “among.” A meta-analysis examines the wealth of information on a topic and synthesizes the results.

In the Stanford study the researchers searched for studies that would allow them to compare “health effects” of organic vs. non-organic foods. They found 17 studies about humans and 223 studies about nutrient levels and contaminants in foods.

Their task was to delve into each study and compare results with results.

Next, researchers need to determine how “significance” is established. In other words, if they find a difference in, say, levels of contaminants, how do they know whether the difference is truly significant?

Establishing significance can be tricky because there are statistically significant results and there are substantively significant results. Statistical significance usually means you want to know whether there’s a difference that might happen just by chance, or whether something actually causes an effect in something else—that it’s “causal.”

In this case, the researchers found very little of significance to report—both statistically and substantively. Bear in mind that their findings are limited to studies already in existence: they drew their conclusions from prior studies.

The found no significant differences in allergic differences among humans but the results came from just 3 studies: a small body of information. They also found lower pesticide levels in children’s urine when they compared organic with conventional diets but—again—the information comes from very few studies: only 2.

They found no significant differences in serum (blood), urine, breast milk and semen in adults when they compared diets.

Turning to the levels of contaminants in food, they did find that organic food was lower than conventional food in pesticide residue, as you would expect. They interpreted the difference as about 30%; meaning pesticide residue levels were 30% lower in organic foods. But is this difference beneficial or harmful? The answer: we don’t know.

Finally the study found that no matter how the animal was raised, chickens and pigs had an equal share of bacteria. But they did find that the conventionally raised chicken and pigs had more antibiotic-resistant bacteria than the organic meat.

We don’t know, however, what effect—if any—this has on humans who consume meat that comes from animals who have more antibiotic-resistant bacteria than other animals.

And the researchers’ motivations?

Turns out one of the chief authors—a Stanford medical doctor–wanted to answer a question she gets from her patients: Is organic food better for you?

Dr. Dena Bravata told the Associated Press she was surprised by the results. “There isn’t much difference.”

For a summary of the study go to http://annals.org/article.aspx?articleid=1355685