From 463a466d7c057eab8d8957b40efbdc379d854a76 Mon Sep 17 00:00:00 2001 From: Vahid Ahmadi Date: Wed, 27 May 2026 11:50:02 +0200 Subject: [PATCH] Add PIP point system planning doc (#1069) #1069 references SI 2013/377 Part 2 (daily living activities and points) and asks for the underlying point system to be modelled. Currently PolicyEngine UK reads the category (STANDARD / ENHANCED / NONE) directly via pip_dl_category and pip_m_category and multiplies by the weekly rate. That's correct for population aggregates because the FRS doesn't capture activity-level scores and DWP's caseload publications report bands rather than scores. Where the points machinery would matter: descriptor reforms (e.g. the 2024 Green Paper proposals), threshold reforms (raising the 8/12 cutoffs), and any analysis distributing by activity. Three-phase plan: 1. Points-to-category mapping behind a use_point_system switch parameter, preserving the categorical default (10 daily-living activity scores + 2 mobility activity scores -> total -> band via threshold params). 2. Descriptor-level parameters under gov/dwp/pip/descriptors/ so descriptor point values themselves are reformable. 3. Data-side descriptor imputation in policyengine-uk-data (needed to make Phase 2 reforms work on the calibrated microsim). Pure planning; current pip variables and parameters unchanged. --- changelog.d/1069.md | 1 + docs/book/programs/gov/dwp/pip-points-plan.md | 143 ++++++++++++++++++ 2 files changed, 144 insertions(+) create mode 100644 changelog.d/1069.md create mode 100644 docs/book/programs/gov/dwp/pip-points-plan.md diff --git a/changelog.d/1069.md b/changelog.d/1069.md new file mode 100644 index 000000000..fdf62f3ec --- /dev/null +++ b/changelog.d/1069.md @@ -0,0 +1 @@ +- Add a PIP point system planning docs page at `docs/book/programs/gov/dwp/pip-points-plan.md` capturing the SI 2013/377 activity-and-descriptor scoring rules and proposing a three-phase implementation route (points-to-category mapping behind a `use_point_system` flag, descriptor-level parameters, then data-side descriptor imputation) that preserves the current categorical PIP model by default. diff --git a/docs/book/programs/gov/dwp/pip-points-plan.md b/docs/book/programs/gov/dwp/pip-points-plan.md new file mode 100644 index 000000000..c14fdcabb --- /dev/null +++ b/docs/book/programs/gov/dwp/pip-points-plan.md @@ -0,0 +1,143 @@ +# PIP point system (planned) + +```{warning} +**Not yet modelled.** PolicyEngine UK currently takes the PIP daily-living +and mobility **band** as a categorical input (`pip_dl_category` and +`pip_m_category`, each `STANDARD | ENHANCED | NONE`) and multiplies by +the published weekly rate. The **points-system** logic that determines +which band a claimant falls into — 0–12 daily-living activities and 12 +mobility activities, scored from the legislation — is **not** modelled. +This page captures the proposed scope, tracked under +[#1069](https://github.com/PolicyEngine/policyengine-uk/issues/1069). +``` + +## What PIP scoring actually is + +The Personal Independence Payment is awarded on a **points-based** +assessment defined in [SI 2013/377][si-377] (the Social Security +(Personal Independence Payment) Regulations 2013): + +- **Part 2: Daily living activities** — ten activities (preparing food, + taking nutrition, managing therapy, washing and bathing, managing + toilet needs, dressing and undressing, communicating verbally, + reading and understanding signs and symbols, engaging with other + people face-to-face, making budgeting decisions). Each activity has + a set of descriptors with point values from 0 to 12. +- **Part 3: Mobility activities** — two activities (planning and + following a journey, moving around). Same descriptor-based scoring. + +The award rule: + +| Total points (per component) | Award | +|-----------------------------|-------| +| 0–7 | None | +| 8–11 | Standard rate | +| 12+ | Enhanced rate | + +Daily living and mobility are scored independently — a claimant can be +on standard daily-living and enhanced mobility, or any other +combination. + +## Why the current categorical model is reasonable for microsim + +For population-aggregate simulation, the categorical bands are +sufficient because: + +- the FRS doesn't capture activity-level point scores at all, +- DWP's published caseload reports band counts (standard / enhanced) + rather than activity scores, +- the calibrated `pip_dl_category` / `pip_m_category` in + `policyengine-uk-data` are derived directly from FRS reported PIP + payments and DWP outturn caseload. + +So for headline distributional and fiscal analysis the categorical +inputs are correct. + +## Where the point system would matter + +Three reform scenarios that the categorical model can't answer: + +1. **Activity-level descriptor reform** — e.g. the 2024 Conservative + Green Paper proposed restricting points awarded for descriptors like + "needs prompting to prepare food". A categorical input can't capture + this; the categorical band wouldn't shift unless an analyst manually + re-bands a synthetic distribution. +2. **Threshold reform** — changing the band thresholds (e.g. raising + the standard-rate floor from 8 to 10 points). Same limitation. +3. **Targeted analysis by descriptor** — distributional questions like + "how does the enhanced cohort split between mobility activities" need + the underlying activity scores. + +## Proposed scope + +### Phase 1 — points-to-category mapping + +- Add the threshold parameters under `gov/dwp/pip/`: + - `daily_living/standard_threshold.yaml` (8) + - `daily_living/enhanced_threshold.yaml` (12) + - `mobility/standard_threshold.yaml` (8) + - `mobility/enhanced_threshold.yaml` (12) +- Add per-activity score inputs as `pip_dl_activity_1_score` ... + `pip_dl_activity_10_score`, `pip_m_activity_1_score`, + `pip_m_activity_2_score`. Type: integer (Person, YEAR), default 0. +- Add derived variables `pip_dl_total_score` and `pip_m_total_score` + summing the activity scores. +- Add `pip_dl_category_from_points` and `pip_m_category_from_points` + that look up the band from the total score against the threshold + parameters. +- Keep `pip_dl_category` / `pip_m_category` as the **input** the rest of + the model reads, with a new switch parameter + `gov.dwp.pip.use_point_system` (default `false`) that, when `true`, + overrides the categorical input with the points-derived band. + +This is a strict superset of the current model: the categorical input +remains authoritative by default, and analysts opting into the points +machinery (for reform analysis) get the activity-level surface. + +### Phase 2 — descriptor-level parameters + +- Per-activity descriptor tables under `gov/dwp/pip/descriptors/`, + encoding the point value of each descriptor in SI 2013/377. The + representation can be flat (one YAML per activity with a list of + `(descriptor_id, points)` entries). +- A `pip_dl_activity_1_descriptor` (etc.) enum input that selects which + descriptor applies; the activity score is then a parameter lookup. +- Reform-side: descriptor point values are then parameters that can be + perturbed for "what if descriptor X scored 4 instead of 6" analyses. + +### Phase 3 — data-side imputation + +- The FRS provides PIP payment amounts but not descriptor selections. + `policyengine-uk-data` would need to impute descriptor selections per + claimant that are consistent with the observed band. The plausible + approach is to draw uniformly across descriptor combinations that + sum to the observed band, weighted by DWP-published "activities most + commonly scoring above zero" tables. +- This phase is the heaviest and is only required to make Phase 2 + reforms work on the calibrated microsim. For the household + calculator, users can input activity scores directly. + +## Open questions + +- Should the score inputs default to `None` (sentinel) or 0? Sentinel + is cleaner when the points machinery is opt-in via the + `use_point_system` flag. +- DWP's PIP review process distinguishes "ongoing" vs "fixed-term" + awards. Should the model expose the award duration, or treat all + current awards as ongoing? (Current model assumes ongoing.) +- The 2024 Green Paper considered moving some of the highest-points + activities to a separate disability benefit — should the design + anticipate that? + +## References + +- [The Social Security (Personal Independence Payment) Regulations 2013 (SI 2013/377)][si-377] — Parts 2 and 3 define the point system. +- DWP, [Personal Independence Payment: Assessment guide][assess-guide]. +- DWP, [PIP statistics](https://www.gov.uk/government/collections/personal-independence-payment-statistics) — caseload by component and band. +- DWP, [Modernising support for independent living: the health and disability green paper (April 2024)][green-paper] — proposals to restrict descriptors. +- Issue: [#1069](https://github.com/PolicyEngine/policyengine-uk/issues/1069). +- Existing model: `pip_dl_category`, `pip_m_category`, `pip_dl`, `pip_m`. + +[si-377]: https://www.legislation.gov.uk/uksi/2013/377 +[assess-guide]: https://www.gov.uk/government/publications/personal-independence-payment-assessment-guide-for-assessment-providers +[green-paper]: https://www.gov.uk/government/consultations/modernising-support-for-independent-living-the-health-and-disability-green-paper