Which statement correctly distinguishes a random sample from a convenience sample?

• A. Random sample minimizes bias; convenience sample guarantees representativeness.
• B. Random sample gives every member a known nonzero probability of selection; convenience sample is selected for ease.
• C. A random sample guarantees representativeness of the population.
• D. A convenience sample has zero bias.

Answer: (B)

The key idea here is how people are picked and what that means for bias and how well the sample represents the whole population. A random sample ensures that every member of the population has a known nonzero chance of being chosen, often the same chance for everyone. This setup makes it possible for the sample to reflect the population on average and lets us quantify sampling error. A convenience sample, chosen simply because it’s easy to reach, doesn’t give everyone a fair shot at being included, so it can be biased toward the characteristics of those who are easiest to recruit and may not represent the population well.

So, the best statement is that a random sample provides a known, nonzero probability of selection for each member, while a convenience sample is picked for ease. The other ideas are misleading: random sampling reduces bias but does not guarantee zero bias or perfect representativeness; a random sample does not guarantee representativeness; and a convenience sample is not free from bias.