The linked study (and the Merten's study it's built ontop of) classifies defaults as "structural" interventions. In the linked meta-analysis, after stripping ou

The linked study (and the Merten's study it's built ontop of) classifies defaults as "structural" interventions. In the linked meta-analysis, after stripping out estimates of publication basis, structural interventions have the most "robust" evidence left (95% CI of 0.00-0.43), and as their paper text says "whereas the evidence is undecided for “structure” interventions". Other structural interventions include, making it easier to select the desired outcome (or make it harder to switch away from desired out come), changing the range of options to facilitate evaluation, or trying to compensate for biases and loss aversion in choice structure. As you can see, this is a broad range of interventions. A little bit further they say "However, all intervention categories and domains apart from “finance” show evidence for heterogeneity, which implies that some nudges might be effective, even when there is evidence against the mean effect", which makes sense. People understand stakes generally, and will likely apply different care/effort in different context, modifying the context specific effect of any given intervention. I think the paper makes a reasonable argument: 1. There is significant publication bias in nudging studies 2. The effect of providing additional information at time of selection, or providing reminders/affirmations for self control is basically non-existent 3. The effect of modifying choice structure is indecisive. Likely we'll find that some structural modifications have strong effects in some context, but others have little or no effect is other context.