I don't know how others do it as a billing service, but, my PM software has a "clinic details" report. It shows amount billed, amount collected, amount written off. Month by month, quarter by quarter. I can print last year's and compare it to this years.
One thing I will say about figures is that billing appropriately and figuring out what you EXPECT to get makes the numbers better and helps the doctor anticipate what's coming.
For instance, say you bill $100 for a new patient exam (to all insurances), each insurance company has their own allowed amount. You need to make sure you know what those amounts are and who the majority of your payors are. Example (for us) B/C pays $30.56, B/S pays $72.45, M/C pays $0, PI pays 100%. So a 50% write off for this code is NORMAL. If your billed out $10,000 and collected $5,000 that's NORMAL, any more or less than that and you need to look at what's happening. Did your insurance base change?
If the patients aren't paying their co-pays or deductibles, or claims are unpaid for mistakes, that's a hard hit. So, again, look at billed/received/write offs.
Hope that makes sense, and helps in some way!