Improving QBID inputs on a per-PUF-line-item basis

[MaxGhenis]

Our QBID inputs are currently very simple:

• QBI includes all of (and only) Schedule C, partnership/S-corp income, Schedule F, and farm rent
• We assume all businesses are qualified and none are SSTB
• We assume a flat ratio of $0.101 W2 wages per $1 QBI

Issues #236 #109 #234 #235 aim to address this.

I asked o3 to take each potential contributor to QBI in the PUF, and assign it the relevant measures we can use to improve these simultaneously, including with standard errors we can use to get stochasticity--critical for these nonlinear policies. Here's its result:

PUF variable	Main activity (Form line)	a. QBI share	b. SSTB share	Mean (QBI ÷ W-2)	SD (QBI ÷ W-2)	Mean (QBI ÷ UBIA)	SD (QBI ÷ UBIA)
E00900	Sch C non-farm sole props	0.80	0.20	0.70	0.35	0.25	0.10
E02100	Sch F farms	0.95	0.00	0.80	0.30	0.15	0.06
E26270	Partnership + S-corp ordinary income	0.85	0.15	0.90	0.50	0.20	0.10
P25700 / E25850	Rental real-estate net income	0.40	0.00	8.00	6.00	0.04	0.02
E27200	Farm-rental (Sch E Part V)	0.50	0.00	5.00	3.00	0.05	0.025
E26390–E26400	Estate & trust net income	0.50	0.10	0.90	0.45	0.20	0.10
E02000 (residual)	Royalties / REMICs / misc.	0.10	0.00	12.0*	10.0*	—	—

These also don't have to be perfect, since we can calibrate to total QBID and its tax expenditure. Getting a reasonable shape and stochasticity of the distribution will enable calibration to hit what we need.

[MaxGhenis]

Three options for representing this in us and us-data:

1. One qualified business income concept assigned in us-data: mirrors taxsim, could require refactoring some state versions
2. Single business_is_qualified, which we could assign in us-data based on composition of income sources - might require assigning based on tax unit composition
3. Add bools for each income source (e.g. schedule_c_would_be_qualified) indicating that it's qualified, then calculate QBI by taking the dot product of each flag and the amount in -us

Per conversation with @baogorek and @PavelMakarchuk, we'll go with option 3.