{"version":"v3","units":{"motorMiles":"Vehicle miles, not million miles; road travel within the authority, including non-residents","rate":"Collision events per 100,000 motor vehicle miles","sharePct":"Modelled vehicle share in percent, not observed use","ratio":"D10 rate / D1 rate"},"nulls":"Null or blank means unavailable. Zero collisions with positive mileage is a valid zero and has a positive upper confidence limit.","grain":{"authorityYear":"One current authority code × year; excluded rows retained","decile":"Parking measure × mapping × scenario × allocation × period × outcome × authority decile","membership":"One authority per parking-measure/scenario combination, frozen over all years"},"definitions":{"scope":"Exploratory English authority analysis on ALL public roads. Numerator: all police-reported injury collisions, including non-motor-only collisions; denominator: DfT all-motor vehicle miles. This is an area-level event frequency measure, not per-driver collision probability or a matched residential/motor-only cohort.","geography":"LSOA21 estimates are assigned using the ONS UTLA23 best-fit lookup. Exact authority codes join to current-highway-authority collision counts and year-specific traffic. No LSOA mileage is inferred. Barnsley and Sheffield code differences remain excluded rather than name-matched.","cohort":"Balanced authority cohort with valid parking lookup and collision/mileage reconciliation in every year 2021–2025. An authority failing any year is excluded from every year, avoiding changing composition. No outcome magnitude is used to select deciles.","parking":"For each authority, sum modelled off-street (or inside-garage) vehicles over LSOAs and divide by total modelled vehicles. Reuse all 27 frozen Phase 2 variants at their published numeric precision. These parking shares are unvalidated proxies.","deciles":"Rank the fixed included authorities by parking share with equal authority weights. Cutpoints at ceil(N*d/10); ties stay together in the lower decile. Freeze the same membership across years within each scenario. These are AUTHORITY deciles, not the Phase 2 LSOA deciles.","rates":"100,000 * summed collisions / summed motor vehicle miles on the same included authority-years. Never average authority rates. Unknown parking status remains in total collisions and mileage; recorded parked involvement is a lower count, with an upper sensitivity count assuming every unresolved case involved a parked vehicle.","uncertainty":"Per-decile 95% exact Poisson (Garwood) intervals condition on fixed traffic estimates and ignore spatial clustering/overdispersion. D10/D1 also has a 95% percentile authority bootstrap: 2,000 samples within the two fixed bins, with all years for an authority resampled together. Neither interval covers parking measurement error, traffic estimation error or systematic under-reporting.","contrast":"D10/D1 = highest-parking decile rate divided by lowest-parking decile rate. Poisson ratio interval uses log-rate approximation. No hypothesis-selection correction or causal interpretation. The scenario envelope is not a confidence interval.","london":"Additional pooled sensitivity removes London and re-ranks the remainder. This checks geographic concentration, not confounding adjustment. Urbanity, road mix, deprivation, housing and vehicle ownership still require Phase 4 controls.","time":"Retrospective descriptive comparison: 2024 EHS rates are applied to 2021 household populations, then compared with 2021–2025 outcomes. Annual consistency is not out-of-time predictive validation. 2021 is pandemic-affected.","limits":"STATS19 excludes damage-only collisions. A parked vehicle being involved does not establish contact, fault or causation. Missing involvement coding varies by authority/year. Residential LSOA frequency and independently observed garage-use effects remain untested."},"notes":"Authority bootstrap intervals apply only to the D10/D1 contrast. Decile chart intervals are conditional Poisson. Exact unrounded source miles drive calculations; display miles rounded to millions. No LSOA rate is supplied."}