In random sampling, what is a key feature regarding the selection of units?

In random sampling, a key feature is that each unit has a known probability of being selected. This characteristic is essential because it ensures that the sampling process is unbiased and that every individual or unit in the population has a fair chance of being included in the sample. This known probability is crucial for statistical analysis as it allows researchers to make inferences and generalize findings to the entire population based on the sample data.

Having a known probability of selection facilitates the calculation of confidence intervals and other statistical measures that require an understanding of how representative the sample is. This systematic approach contrasts sharply with methods where selection might rely on preferences or convenience, which could introduce biases into the research and compromise the validity of the results.

In summary, the correct answer underscores the importance of establishing a fair and objective mechanism for selecting sample units, which is foundational to achieving reliable outcomes in marketing research.