用于总结研究的局限性

Based on the article provided below, write a concise paragraph (3–5 sentences) identifying the main limitations of the study.

The limitations should:
- Be specific to the study design and methods used
- Focus on potential weaknesses in experimental design, measurement, sampling, or analysis
- Avoid speculative or overly generic limitations
- Be written in an academic, human tone suitable for the Discussion section

Where relevant, consider issues such as:
- study design constraints (e.g., observational design, short follow-up)
- sample characteristics or representativeness
- measurement error or construct validity
- unmeasured confounding or residual bias
- limited generalisability
- analytical or modeling assumptions

Here is the article:
[PASTE ARTICLE OR SECTION HERE]