There isn't a single accepted valuation formula. I looked into partnership several years back but declined because the price was too high. Still work at the same place as an employee with an adjusted contract so I get a flat percentage of all the revenue I produce.
The older ophthalmologists in my town are having great difficulty unloading their practices. Our practice owner has been trying unsuccessfully for over 10 years. Others in the area in their mid to late 60s are having the same basic problem: they think it's still 1985 and believe their practices are worth 2 million dollars while the potential buyers aren't even wanting to pay a quarter of that price.
If anything, I'd rather start my own practice for a fraction of the cost.