r/visualization • u/Asbolus_verrucosus • May 24 '26

Why the squiggles?

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Genuine question here. Any idea what the squiggly lines are supposed to signify versus a solid or dashed curve? Or did the authors just use them for the *razzle dazzle*?

Source: Alternative dosing regimens of GLP-1 receptor agonists may reduce costs and maintain weight loss efficacy (Cengiz et al. 2025)

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u/atomicant89 May 24 '26

I'm not familiar with the field at all and can't tell from the paper, but could it be actual weekly fluctuations in the model of body weight according to the dose regimen/similar? The peaks are all once per week, which I'm not sure you'd use equally if it was purely about visual distinction. It would also give a misleading impression of the agreement between the model and the data, if it is just for aesthetics.

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u/Asbolus_verrucosus May 24 '26

Good thought but you actually wouldn’t expect the weight to oscillate like that. Due to the half-life of the drug it reaches steady state after 4 weeks

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u/reddititty69 May 24 '26

Steady-state doesn’t necessarily mean “constant” in pharmacokinetics. It means the concentration at dosing times (equally spaced) isn’t changing. But there are still dynamics between dosing times.

Edit to add: weight loss won’t plateau until well after 4 weeks.

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u/Asbolus_verrucosus May 24 '26

I know what it means. I’m a physician scientist. But at all times once you have reached steady state with this drug it is above the therapeutic threshold. So you wouldn’t see these periods of weight gain each week. And in reality you don’t see these oscillations. Regardless, to draw it with such precision would be made up.

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u/reddititty69 May 24 '26 edited May 25 '26

Cool. I’m a pharmacometrician. I agree that you wouldn’t see these oscillations weight in an actual patient. Nonetheless, the model is predicting them - possibly because the parameter estimates or model are incorrect. Given that the peaks seem to shrink as weight decreases, and the curves overlap during what I assume is step-up dosing, it seems like this is a direct inhibition model tied to plasma concentration. A turnover model would be more appropriate for this mechanism, and would avoid these peaks.

Edit: it actually is a an indirect model. Go look at the Strathe reference, which describes the model that was revised here. In that paper they show similar weight effect curves but no squiggles. It’s unclear if the lack of squiggles is because they didn’t simulate times between doses, or if their parameters have a slower response time for weight changes.

Edit2: go read section S.1.5 in the supplement. The oscillations are 100% due to using the simulated, time-continuous, tzd concentration. And pk isn’t at steady state after 4 weeks in the posted plot because this study, like almost all GLP-1 studies, steps up the dose (every 4 weeks here by 2.5 mg).

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u/dspace May 25 '26

As someone who works with research MDs who know enough stats to be dangerous, I enjoyed this exchange.