Roll forward student loan plan types on uprating#271
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nwoodruff-co wants to merge 3 commits intomainfrom
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Roll forward student loan plan types on uprating#271nwoodruff-co wants to merge 3 commits intomainfrom
nwoodruff-co wants to merge 3 commits intomainfrom
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When uprate_dataset advances a dataset to a future year, re-derive Plan 1/2/5 assignments from age using the target year. A 20-year-old in the 2023 FRS simulated in 2029 gets uni_start_year = 2027 → Plan 5, rather than remaining frozen at their 2023 Plan 2 assignment. Plan 4 (Scotland) and Postgraduate are left unchanged as they cannot be inferred from age alone.
Data build (student_loans.py): - Replace repayments > 0 imputation with age-cohort participation rates - Assigns Plan 1/2 to all outstanding borrowers (incl. below threshold) - Calibrated to ~3.5M GB Plan 1 and ~5.9M GB Plan 2 total holders (2023) - Highest-income selection within each age group Uprating (uprating.py): - Plan 1: mechanistic write-off using 25-year loan term rule (exit if age >= 2069 - target_year), declining to zero by 2035 - Plan 2: forecast-calibrated targets from DfE student loan forecasts (England), scaled to GB and FRS coverage (55.9%) - Plan 5: same DfE forecast calibration for post-2023 cohort - All plans within ~5% of DfE targets throughout 2024-2034
DfE forecast shows Plan 2 total borrowers growing throughout the forecast window (40-year write-off, no significant decline until ~2055). Updated _PLAN_TARGETS to reflect gentle growth to ~7M peak then very modest decline, rather than the incorrect steep post-2030 drop. All three plans now within 4-5% of DfE targets 2024-2034 (well within the 10% tolerance), with Plan 2 flat/growing and Plan 5 correctly ramping up from near-zero to ~5.7M by 2034.
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Summary
uprate_datasetadvances a dataset to a future year, student loan plan types (Plan 1/2/5) are now re-derived fromageusingtarget_year - age + 18against the historical cutoffsTest plan