With probability sampling, each unit in the survey population has a known, positive probablity of selection. This property of probability sampling avoids selection bias and enables you to use ...

If no other sources are available to measure certain variables of a target population, Statistics Netherlands often uses a random sample, i.e. a sample of units from the population drawn in accordance ...

Therefore, this study uses a stratified clustered sample design. The primary sampling units, or clusters, are study groups. The list of all study groups in the school is stratified by grade level.