Temporal and within practice variability in the health improvement network.

Area of Science:

• Epidemiology
• Health Informatics
• Pharmacoepidemiology

Background:

• The Health Improvement Network (THIN) is a UK primary care electronic medical record database used for pharmacoepidemiologic research.
• Standard methods like matching on practice and calendar year are used to control for temporal and practice-specific differences.
• Limited understanding exists regarding the consistency of data within practices over time and among different practices.

Purpose of the Study:

• To assess the consistency of THIN data within practices across years and among practices within a year.
• To quantify secular trends and practice variations in key health metrics.
• To inform the design of pharmacoepidemiologic studies utilizing large electronic health record databases.

Main Methods:

• Analysis of mortality, cancer incidence, prescribing, and encounter rates from 2000-2007 using 415 UK practices.
• Longitudinal Poisson regression models (random and fixed effects) with practice-year as the unit of observation.
• Adjusted models incorporated practice-level characteristics like smoking, obesity, age, and software experience.

Main Results:

• Significant linear trends (p < 0.001) were observed: decreasing mortality, increasing cancer reporting, increasing prescriptions per patient, and decreasing encounters per patient over calendar years.
• In 2007, the interquartile range (75th to 25th percentile ratio) for crude rates was 1.63 for cancer and mortality, 1.45 for prescriptions, and 1.42 for encounters.
• Accounting for practice characteristics reduced the variation among practices by approximately 40%.

Conclusions:

• THIN data exhibit significant secular trends and substantial variation among practices.
• These temporal and practice-specific variations must be considered when designing pharmacoepidemiologic studies.
• The study could not definitively distinguish whether observed trends reflect data quality changes or true secular health trends.