10% for "somewhat likely" wouldn't make any sense, "likely" by itself means >50%. I was proposing to simply label 5 or 7 points on the slider, like 10% as "very unlikely", 50% as "neutral", and 66% as "somewhat likely". I am sure there is a decent-sized study that asked people to predict events on a Likert scale as likely/unlikely and then one could calibrate the mapping from Likert scale to probability points using this study. There is a study showing that people intuitively map Likert scales to a slider https://link.springer.com/article/10.3758/s13423-017-1344-2/... so by properly spacing and positioning the Likert labels, people will at least be somewhat more calibrated than in the absence of any cues.
It does make sense for some people. Some people might say it's somewhat likely Sweden is still not a NATO member at the end of the year – and mean there's a 10 % probability it happens.
That's the problem with these fuzzy labels – the variance between individuals (and even within individuals across time) is huge.
