Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2026 Sep 7;14:1896650. doi: 10.3389/fpubh.2026.1896650

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

Copyright © 2026 Bu, Zhu, Zhao, Xu and Song.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

PMC Copyright notice

Flowchart illustrating the selection process for surveillance records from 2020 to 2024, starting with 107,441 records. After applying exclusion criteria—such as BMI outside 12–50 kg/m², age outside 15–35 years, incorrect grades, and insufficient records per class-year—980 records are excluded, resulting in a final analytical sample of 106,461 records across 2,591 class-year units. Counts per year: 17,302 (2020), 18,195 (2021), 23,003 (2022), 23,484 (2023), and 24,477 (2024), with respective class-year unit counts provided. — Flow of records through data integration and cleaning (107,441 → 106,461 records analysed in 2,591 class-year units), with the by-year breakdown of the final sample.