What are the metrics?

There are many fields of study that seem to lack useful metrics by which to judge their usefulness and effectiveness.

Nutrition science, see below, is certainly one example. Epidemiology and the Covid pandemic is another. There are others. The problem is that experts seem to rarely acknowledge that their past work was insufficient, flawed, ineffective. Instead of learning from the past, they tend to double down on what did not work previously (see, Covid-19).