Table 1_Same ICD-10 code, different estimands: four Polish National Health Fund obesity series, 2015–2025.docx

Although their labels suggest related measures of obesity, differences in analytical unit, entry rule, look-back period, and temporal structure may alter both the reported level and the apparent response to healthcare-system disruption. We examined whether selecting an official NFZ E66 series materially changes the level, trend, and permissible public-health interpretation of recorded obesity-related activity.</p>Methods<p>This retrospective, descriptive ecological time-series study audited 44 annual resources covering registered morbidity, first-recorded patients, annual E66 patients, and E66-coded services in 2015–2025.

We analyzed counts and population-scaled administrative rates, summarized long-term change using log-linear annual percentage change (APC), and used a one-year 2020 indicator as a descriptive pandemic-era stress test. An endpoint sensitivity analysis excluded 2025. Independent BMI sources provided cross-sectional contextual triangulation for 2025.</p>Results<p>In 2025, two official person-based series yielded 1,534,022 persons with a current or earlier principal E66 record and 325,769 persons with qualifying current-year E66 activity, a 4.7-fold difference arising from construction rather than alternative estimates of a single quantity.