Opponents of mandatory labeling of GMO foods often argue that requiring mandatory labels could mislead consumers - making them think there is a safety risk when the best science suggests the opposite. This is no minor issue, as citizens in Oregon and Colorado will vote on mandatory labeling initiatives this November (previous voter initiatives in California and Washington narrowly failed; legislation in Vermont has already passed).
Here, for example, is an unlikely critic of mandatory GMO labeling, Cass Sunstein (Obama's former "regulatory czar") writing for Bloomberg.com:
I have made related arguments in the past, and have even published some prior academic work giving some empirical evidence backing the concern. However, the evidence is far from conclusive.
Marco Constanigro at Colorado State University and I decided to investigate the issue more directly in a couple studies we conducted last year, which are now published in the journal Food Policy.
Our research strategy sought to determine whether consumers who were exposed to foods that had GMO labels subsequently indicated higher levels of concern than people who hadn't been shown such labels.
In the first study, we used apples as the context. Respondents were randomly assigned to one of three groups. One group (the control) made choices between apples that did not mention GMOs at all - that had a decoy attribute: ripening with ethylene. Another group made choices with mandatory ("contains") GMO labels, and another group with voluntary ("does not contain") labels. The following shows examples of choices we presented to people in the control and treatment groups.
After making several choices between apples like this with different labels, then we asked each set of consumers a bunch of questions about how safe they thought it was to eat GMOs, how concerned the were about GMOs relative to other issues, etc.
Here's the first key result: There was no consistent statistically significant difference in the average level of concern for GMOS expressed by people shown different labels. That is, the mere presence of the GMO label did not lead to a greater level of concern about GMOs.
However, we can also study the actual apple choices that people made, and use those choices to infer aversion to GMOs. And here, another set of interesting results emerges: Consumers' willingness-to-pay to avoid GMOs is more than twice as high in the presence of mandatory "contains" GMO labels as compared to voluntary "does not contain" GMO labels. Also, willingness-to-pay to avoid ethylene ripening (a common, and heretofore uncontroversial, industry practice) is as high as that to avoid GMOs.
In the second study, respondents were divided into one of two groups. The first control group was shown an unaltered box of cheerios and was simply asked to click on the areas of the box they found most and then least appealing. A second treatment group did the same but for a box of cheerios that had, in small print on the bottom left-hand-side of the package the label "partially produced with genetic engineering." After looking at these packages, we then asked each set of respondents a series of questions about how safe they thought it was to eat GMOs, how concerned the were about GMOs relative to other issues, etc. The idea is that if GMO labels signal safety then those people who say the mandatory label should subsequently indicate a higher level of concern than those who did not see such a label.
Here are "heat maps" associated with the initial the results where we simply asked people to click on the areas they found most/least desirable. The top pictures show the clicks for most desirable and the bottom pictures the clicks for the least desirable (clearly people in the GMO treatment noticed the GMO label and found it unappealing):
Here's the key result: There was no statistically significant difference in the level of concern for GMOS expressed among people shown the box with the GMO label vs. the group shown the box without the GMO label.
Thus, neither study supported our hypothesis that the mere presence of GMO labels would lead people to believe GMOs are more or less safe.
Here's how we concluded the paper: