Researchers often face challenges in covering an entire population under investigation and must instead focus on a subset. This paper applies different sampling theory methods to estimate parameters related to mental health disorders across different countries. Various techniques and methods of sample selection exist, leading to various types of samples. This paper aims to apply sampling theory methods to analyze the relationships between features that represent different mental disorders. The aim is to identify the sampling method that minimizes the variance of the studied characteristics’ mean and generates a representative sample of a whole population. Additionally, the goal is to determine which feature predominantly influences global trends in mental health disorders.