Three important principles of sampling survey are:

1. Principle of validity

2. Princilpe of statistical regularity

3. Principle of optimization

when there are errors in sampling design, such as biases in selecting participants or a non-representative sample, which can lead to inaccurate results.

28,000

Standing in a shooping mall and selecting people as they walk by to fill out a survey is an example of convenient sampling.

Quotas are useful especially in sampling when selecting survey participants.