Simplifying Raw, Adjusted and Weighted Population List Sizes | A Guide for Primary Care Network Leaders

We were recently asked if we could point someone in the direction of an explanation of what raw, weighted, and adjusted populations mean. It's a great question and one we probably should have answered ages ago.

Whether you're experienced or new to your role, here's a straightforward breakdown of how different population measures affect NHS funding and budgets.

I have even included a little quiz to help you retain this information.

This guide was developed using information from NHS England ICB Allocations documentation and NHS England PCN Adjusted Populations guidance.

At THC Primary Care, we provide resources to primary care network leaders. 

Let's jump in!

Core Concepts - Simplified Definitions

Raw Population List: The actual count of patients registered with a practice or PCN without any modifications.

Adjusted Population List: Raw counts modified to account for practical circumstances such as PCN membership changes or eligibility requirements.

Weighted Population List: Population counts that have been mathematically adjusted to reflect varying healthcare needs across different demographic groups.

At-a-Glance Comparison

Feature	Raw List	Adjusted List	Weighted List
Basic definition	Simple headcount of registered patients	Headcount modified for PCN membership and eligibility	Population count adjusted for healthcare needs
Primary purpose	Tracking patient numbers	Fair administrative representation	Equitable funding allocation
How each patient is counted	1 patient = 1	1 patient = 1 (list changes based on PCN membership)	Patient value varies based on need (can be >1 or <1)
Key data source	PCSE GSUM Capitation Reports	GSUM + ODS ePCN file	Multiple need indicators + formulas
Complexity	Low	Medium	High
Main PCN use	Capacity understanding	Contract management & eligibility	Resource planning and equity
Update frequency	Quarterly	As needed (membership changes)	Annually (funding formula updates)

Detailed Explanations

Raw Population List

Definition and Purpose: Raw population lists represent the actual count of patients registered with a healthcare provider, typically a GP practice. They serve as the foundational data point for understanding your patient population size.

How It's Calculated: It's a simple addition of all registered patients on a practice list, usually taken from PCSE's GSUM capitation reports which are produced quarterly.

When It's Used

• Basic performance monitoring

• Simple capacity planning

• Patient-facing communications

• Setting baseline expectations for resource needs

Key Considerations

• Does not account for patient needs or demographics

• Easiest to understand and communicate

• Updated quarterly through PCSE reports

• Serves as the baseline for further calculations

Example with Numbers: If a PCN consists of three practices with 5,500, 8,500, and 6,000 patients, respectively, the raw population would be 20,000.

Adjusted Population List

Definition and Purpose: Adjusted population lists modify raw counts to account for specific practical circumstances, ensuring fair representation for administrative or operational purposes.

How It's Calculated

1. Start with raw list sizes from a specific reference date

2. Account for PCN membership based on organisation data service data

3. Include patients from non-PCN practices who are still eligible for services

4. Apply adjustments for practices that have changed PCN membership

5. Normalise the results to maintain proper proportionality

When It's Used

• PCN funding allocations

• Practice-level comparisons

• Service coverage planning

• Contract management

Key Considerations

• Changes when practices join or leave a PCN

• Ensures all eligible patients are counted appropriately

• May include patients from practices not formally in your PCN but eligible for services

• More accurate for administrative purposes than raw lists

Example with Numbers: A PCN has a raw population of 20,000, but one practice recently joined from another PCN. The adjusted list would include specific calculations to ensure proper representation of these new patients while maintaining appropriate proportionality across the system.

Weighted Population List

Definition and Purpose: Weighted population lists transform raw counts to reflect the relative healthcare needs of different patient groups, accounting for factors that drive demand and cost.

How It's Calculated: The calculation involves multiple components:

1. Apply demographic and clinical need weightings

2. Apply geographic and cost adjustment factors

3. Normalise to create comparable indices

4. Combine component weightings according to expenditure proportions

5. Calculate overall need index (where 1.0 = average need)

When It's Used

• Fair resource allocation

• Strategic needs assessment

• Funding formula development

• Health inequalities targeting

• Service transformation planning

Key Considerations

• Reflects actual healthcare demand rather than simple headcount

• Accounts for demographic factors (age, gender, deprivation)

• Includes geographic cost variables (Market Forces Factor)

• Provides the most accurate picture of resource requirements

• Highest complexity but most equitable approach

Example with Numbers: A PCN with 20,000 raw patients might have a weighted population of 22,500 if it serves an older population with higher healthcare needs, or 18,000 if it serves a younger, healthier population.

Key Terms Glossary

Technical Term	What It Actually Means	Why It Matters to PCNs
Capitation	System of paying based on number of patients (per head funding)	How most PCN funding is calculated
EACA	Extra costs for ambulance services in rural or congested areas	Relevant for PCNs in very rural or very urban settings
Expenditure Proportions	How much different types of healthcare typically cost	Determines how different factors are weighted in the formula
Global Sum	Core funding for GP practices based on their patient lists	The foundation of practice funding that relies on capitation
Health Inequalities Adjustment	Extra weighting for deprived areas to help tackle unfair health differences	More funding for PCNs serving disadvantaged communities
Market Forces Factor (MFF)	Adjustment that recognises healthcare costs more in some areas (like London) than others	Affects your weighted population if your PCN is in a high-cost area
Need Index	Score showing if your population needs more (>1.0) or less (<1.0) than average	Quick way to see if your population has higher than average needs
Normalising	Rescaling numbers so totals match up (making different calculations comparable)	Ensures fair comparisons between different PCNs

Practical Applications

Using Raw Lists

• Scenario: Understanding your basic capacity needs

• Application: A PCN with 20,000 raw patients can use this figure to calculate basic staffing ratios and physical space requirements.

• Decision guideline: Use raw lists when you need simple headcounts for straightforward planning.

Using Adjusted Lists

• Scenario: Managing PCN contract requirements

• Application: When determining eligibility for specific PCN services, the adjusted list ensures all appropriate patients are included, even if practice configurations have changed.

• Decision guideline: Use adjusted lists when dealing with contractual obligations, PCN payments, or administrative requirements.

Using Weighted Lists

• Scenario: Planning for equitable service distribution

• Application: A PCN with many elderly patients will show a higher weighted population, justifying additional resources for services that meet their specific needs.

• Decision guideline: Use weighted lists when planning services that should reflect actual healthcare demand rather than simple headcounts.

The Quiz

We hope this helps 😊.

Resources and References

For more detailed information, refer to these official resources:

• NHS England ICB Allocations documentation: https://www.england.nhs.uk/allocations/

• NHS England PCN Adjusted Populations guidance: https://www.england.nhs.uk/primary-care/primary-care-networks/

• Organisation Data Service (ODS) ePCN publications: https://digital.nhs.uk/services/organisation-data-service

• Primary Care Support England (PCSE) documentation: https://pcse.england.nhs.uk/

For support with understanding or applying these population measures, contact your local ICB Primary Care team.

We hope this helps 😊.

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