The people that figure out how much money needs to be set aside this year to pay for the defined pension benefit accrued this year are called actuaries. However, the people that sit on the board of the taxpayer funded pension plans are politicians and senior government employee union officials. So the actuary that gives them the result they want is the actuary that gets hired.
These are all guesses based on assumptions, of course, and no one knows the future 5, 10, 20, 30+ years from now. But as an idea of how corrupted taxpayer funded pensions are, the US government requires all non taxpayer funded pensions to calculate the liabilities using yields from highly rated corporate bonds, i.e. a conservative, safe investment class.
However, the US government exempted taxpayer funded pensions from any oversight, and so they can use whatever discount rate they want. For example, private companies have to use ~4% for their discount rate, whereas governments use ~8%+ for their discount rate.
But that's just small pickles. The big problem is there is no enforcement of even the liberal actuarial recommendations that the pension fund pays for. IL/NJ/CT/and other trouble governments simply skip contributions, i.e. don't set any money aside for the future, and that's the main reason they are in this situation. A decade or two ago, the senior union officials on the pension board didn't care about the skipped contribution payments to make a sufficiently big deal out of it, since they were going to get paid in the short term anyway. And they negotiated ridiculous pension benefits which are never seen in the private sector, such as final average pay formulas.
A typical pension formula is years of service * 1% * salary over 30 years (with a cap). That's referred to as a 1% plan, some companies might do 2%, maybe even 3%.
But in the government, you have formulas like years of service3%final average pay for the last year, or 3 years, or 5 years. That is why you see cops and firefighters working 100 hours a week when they're about to retire in their 40s and 50s, so they can secure $100k+ per year defined benefit pensions. You would NEVER see that in the private sector, as that's a laughably unaffordable benefit.
On top of which, police and firefighters in some lavish plans get to retire in 20 years, so if they start at 18 to 22, they're retiring at 38 to 42, and getting paid $100k per year for 40+ years. That's an annuity worth millions of dollars.