[UncleMeat]

Rarely is this salary guaranteed. It often requires TAing to supplement research funding and graduate students are often required to be deeply involved (or even solely responsible) for sourcing their own research funding. Stipends are also often poverty wages or even lower when you consider that stipends are usually only for 3/4 of the year and you are usually expected to continue research during the summer.

I know some folks who did PhDs in non-engineering fields at state universities who had to TA every single semester, often TAing multiple classes, just to earn ~$20,000 per year.