The denominator in general practice, a new approach from the Intego database

Area of Science:

• Epidemiology
• General Practice Research
• Health Informatics

Background:

• Determining the 'population at risk' is a persistent challenge in general practice-based epidemiological research.
• Accurate denominators are essential for calculating reliable epidemiological figures.

Purpose of the Study:

• To demonstrate a method for calculating a reliable denominator (practice population) without an existing patient list.
• To illustrate a novel approach using annual patient contact data from general practices.

Main Methods:

• Utilized the Intego database containing patient contact, diagnosis, and prescription information.
• Calculated the number of patients contacting a practice annually.
• Combined Intego data with sickness fund reimbursement claims to derive a correction factor stratified by age, gender, and district.
• Extrapolated annual contact data using the correction factor to estimate the practice population.

Main Results:

• In 2003, 64,161 patient contacts in the Intego register corresponded to an estimated practice population of 80,094.
• The model for estimating practice population was found to be independent of socio-economic status data.

Conclusions:

• A reliable practice population denominator can be calculated using a correction factor derived from patient contact data.
• This methodology is vital for accurate epidemiological studies in general practice settings.
• The approach is potentially applicable to general practice research in other European countries.