Proving a Point Again on Soda Taxes

When curiosity fades, research ceases to be science and becomes an exercise in advocacy. That advocacy might be for a commercial interest or it might be for a presumably good cause. But in either case, it’s not sound scientific research with the aim of finding the true answer to a clear question. It is a tool for advancing an agenda. A fine example of this surfaced in PLOS Medicine this week. Researchers have a new study in the journal that serves their purpose of proving a point about the effectiveness of soda taxes.

The authors of this paper write that their study of obesity prevalence trajectories “suggest that the UK soft drink industry tax led to positive health impacts in the form of reduced obesity levels in girls aged 10 to 11 years.”

That was good enough for the New York Post, which came up with a punchier headline:

“Soda tax slashes obesity rates in young girls.”

Score one for advocacy, nil for science. Because all this study offers is slim evidence for an association of a trend with the tax in a small subsegment of the population they studied. Not a robust causal relationship.

Digging for Evidence

Like many questions about obesity and nutrition, this is a subject that prompts strong feelings. Some people in the field are certain that soda taxes work. And thus, they are intent on finding evidence for proving this. Others have distinct reasons – some of them financial – for resisting this. So they dig for evidence to prove their points.

Andrew Brown is a scientist who has put considerable energy into the subject of scientific rigor in nutrition and obesity research. He responded to this study, saying:

“I commend the authors for recognizing up front that an interrupted time series analysis has important limitations, such as unidentified co-interventions and time-varying confounding, that they cannot rule out.

“Unfortunately, though, they move on to express increasing levels of certainty, calls to action, and causal interpretation in their conclusions.”

Without Curiosity, It’s Not Science

We should all bring passion to our work. But when that work is science, curiosity is essential. Proving a point about soda taxes is good for advocacy. But without curiosity and openness to discovering the truth about their effectiveness, it’s not science.

This is why some folks are skeptical about industry-funded research. The possibility is real that some of this research exists mainly to prove a commercially useful point. The same problem exists when a researcher seeks to validate a strong belief, without considering that the belief might prove to be false.

And such is the case of much of the research on soda taxes.

Click here for the study in PLOS Medicine, here and here for further perspective

The Money Diggers, painting by John Quidor / WikiArt

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January 28, 2023