This occurs when the sample does not accurately represent the population, often due to poor selection methods. Common Sampling Techniques
Effective sampling relies on specific methodologies to ensure results can be generalized to the entire dataset. Data Collection | Definition, Methods & Examples - Scribbr
For findings to be valid, a sample must accurately reflect the characteristics of the whole population.
The population is the entire collection of elements you want to study, while the sample is the specific group you actually collect data from.