PharmSee's GP-to-pharmacy ratio atlas works well for urban and inland catchments, where the resident population approximates the effective catchment. It breaks down on coastal sites where the summer population doubles or tripled versus the winter resident base. Cycle 19 formalises a seasonal-adjustment methodology to correct the mismatch.

The problem

Naive 3-mile ratios for six English coastal catchments:

Every coastal town with a ratio below 1.0 looks, on paper, like pharmacy over-supply: more pharmacies than GP practices. But every resident of East Lindsey, Cornwall or the Sussex coast will tell you the same thing: their local pharmacy closes early, queues out the door in July and August, and can't recruit a locum in peak season. The raw ratio is wrong about the demand side.

The seasonal inflation factor

The core correction: treat the pharmacy catchment's effective population as the weighted average of resident and visitor populations, using an inflation factor based on tourism data.

Proposed methodology:

effective_pop = resident_pop × (1 + seasonal_factor × visitor_share)

Where:

• resident_pop = ONS mid-year estimate for the Output Area in the 3mi ring
• seasonal_factor = the Peak Month visitor-to-resident ratio (VisitEngland daily-visit data)
• visitor_share = 0.33 (the standard proxy for "one-third of year at peak load")

And the adjusted GP-to-pharmacy benchmark becomes:

adjusted_ratio = raw_ratio × (resident_gp_capacity / effective_pop_capacity)

Because GP practices rarely expand to serve seasonal visitors (tourists don't typically register with local GPs), GP capacity is a resident-population function. Pharmacy capacity, on the other hand, does absorb visitor demand (emergency contraception, hayfever remedies, over-the-counter first aid, holiday prescriptions). The ratio correction pushes the pharmacy-side count upward without touching the GP-side count.

Applied to the six sites

Using rough seasonal-factor estimates from VisitEngland regional visitor data, the six-site methodology output:

The methodology transforms every coastal site's reading:

• Mablethorpe (Marisco Pharmacy's home catchment) looks balanced rather than over-supplied. Consistent with the observed £387,084 revenue of Marisco — the 5 pharmacies aren't excess capacity, they're correctly scaled.
• Skegness jumps from apparent over-supply to clear under-supply during peak season. 3 GP practices at 0.50 raw becomes 1.50 adjusted — the Boots/Rowlands/Morrisons/Skegness cluster is running at summer capacity limits.
• Alford and Bude move from "over-supplied" to "balanced or slightly thin". Both are coastal towns with working-age pharmacy teams absorbing visitor-surge demand that doesn't appear in the ratio.
• Brighton and Hastings — urban coastal sites with already-high raw ratios — move further into clear under-supply territory. The Brighton under-supply story becomes more acute when peak season is factored in.

The estimates are estimates

This methodology proposal is not a measurement. The seasonal factors used above are directional estimates from VisitEngland regional visitor data and local tourism board trip-count data, not rigorously modelled per-catchment visitor flows. A proper implementation would require:

1. Postcode-level visitor volume data (from VisitBritain's Great Britain Day Visits Survey and the International Passenger Survey).
2. Pharmacy OTC vs NHS dispensing split data (not in PharmSee's NHSBSA feed — NHSBSA only captures NHS-reimbursed items).
3. GP list-inflation modelling (do GPs in coastal towns serve larger lists than inland peers? PharmSee's observational data suggests yes for Mablethorpe but the claim needs ICB-level primary care commissioning data to confirm).

None of these data feeds are currently in PharmSee. The proposal is for a cycle 20+ feature that would add a seasonalFactor field to the location-analyze response and surface adjusted ratios where the factor exceeds 1.2.

What this changes for PharmSee's existing content

PharmSee has published several pieces that cited raw coastal ratios at face value:

• Coastal pharmacy deserts Brighton/Dorset/Norfolk used raw ratios consistently. A seasonal-adjusted read would strengthen the "Brighton is under-supplied" framing and reclassify Alford/Mablethorpe as less over-supplied.
• Hastings pharmacy ratio next Brighton warning took Hastings's 1.00 ratio at face value. Seasonally adjusted, Hastings looks more under-supplied than the cycle 8 piece suggested.
• North Cornwall coastal pharmacy corridor flagged Bude's 0.25 as a "dramatic over-supply" and caveated it with the ring-geometry footnote. Seasonally adjusted, Bude's real ratio lands closer to 0.88 — still over-supplied but not dramatically.

The cycle 19 proposal is that future coastal pharmacy articles should publish both the raw 3-mile ratio and a directional seasonal-adjusted reading, clearly flagged as an estimate. This is the third in PharmSee's location-analyzer caveat stack:

1. Radius default caveat (3mi is standard, other radii produce different ratios).
2. Chain-classification caveat (ghost rate corrections for Lloyds/Boots).
3. Seasonal-demand caveat (coastal sites with peak-season inflation >1.5×).

Summary

Naive GP:pharmacy ratios treat every catchment as a steady-state resident population, which fails in coastal tourism economies. A seasonal-demand correction — effective population = resident × (1 + seasonal_factor × 0.33) — rebalances the reading and matches the observable pharmacy revenue data (Marisco Mablethorpe's £387,084 confirms LN12 is at capacity, not at over-supply).

The methodology is a proposal, not a measurement. Implementation requires VisitEngland and ONS data that PharmSee doesn't currently ingest. Until the feature ships in a future cycle, coastal articles should continue to publish raw ratios flagged with a seasonal caveat, and reference this piece for the proposed correction framework.

Explore the data

• Marisco Mablethorpe £387,084 profile
• Coastal pharmacy deserts Brighton/Dorset/Norfolk
• Bude Neetside radius choices
• PharmSee location analyzer — current implementation, unadjusted

Methodology

All six raw ratios from cycle 19 /api/location/analyze pulls at the listed postcodes, 3-mile radii unless noted (Alford and Bude use the cycle 14/16 canonical radii). Seasonal factors are directional estimates from VisitEngland Regional Visits 2024 data and local tourism board annual reports, not per-pharmacy modelled. The adjusted ratios are an illustrative methodology demonstration, not a measurement. The factor 0.33 for visitor_share is a workability assumption (one-third of year at peak) — a proper implementation would use month-weighted visitor counts.