In which sampling method does every member of the population have an unknown and random chance of selection?

In which sampling method does every member of the population have an unknown and random chance of selection?

• A. Systematic Sample
• B. Random Sample
• C. Stratified Sample
• D. Convenience Sample

Answer: (B)

The key idea is that randomness means each member of the population has an equal chance of being chosen, even though you don’t know in advance who will be selected. This is what happens in a simple random (random) sample: every unit has an identical, nonzero probability of inclusion, and the actual selected individuals are determined by a random process. This lack of bias helps ensure the sample is representative and supports valid inferences about the population. Other methods introduce structure that affects who can be chosen. Systematic sampling uses a fixed interval, which can bias the sample if the list has a pattern that aligns with that interval. Stratified sampling ensures representation from subgroups but does not give every individual in the population an equal chance of being selected. Convenience sampling picks whoever is easiest to reach, which is inherently biased.

The key idea is that randomness means each member of the population has an equal chance of being chosen, even though you don’t know in advance who will be selected. This is what happens in a simple random (random) sample: every unit has an identical, nonzero probability of inclusion, and the actual selected individuals are determined by a random process. This lack of bias helps ensure the sample is representative and supports valid inferences about the population.

Other methods introduce structure that affects who can be chosen. Systematic sampling uses a fixed interval, which can bias the sample if the list has a pattern that aligns with that interval. Stratified sampling ensures representation from subgroups but does not give every individual in the population an equal chance of being selected. Convenience sampling picks whoever is easiest to reach, which is inherently biased.