2.4% is way too low.

AFAIK, underemployment is more on the lines of having someone overqualified doing the work at the pay rate of that lower worker.

Eg. A doctor working as a personal support worker.

A doctor would be horrendously over qualified for a job as a PSW, but if they're doing that work for the same pay as a PSW, they're under employed. This is an extreme example, but it demonstrates the point using jobs that I feel most people would be familiar with. If you're not, then the only hint I can give is that I believe the role of PSW used to be and occasionally still is referred to in hospitals as an "orderly".

There's still a non-trivial number of people with doctorates working at places like Starbucks and McDonald's... Who are underemployed, but I'm specifically saying that if you're "employed" but you only get, say, 5 hours a week, and you have to hold four jobs just to clock 30+ hours in a week, or you need four jobs to make ends meet, then that's an insufficiently employed person. IMO, anyone in that situation would be better off on social assistance, where available. Being incapable of finding a full time job or finding a job that will be able to provide full time hours, should be counted.