What does a "random sample" ensure in a research study?

A "random sample" is crucial in research because it ensures that each individual in the population has an equal chance of being selected. This characteristic is fundamental for achieving the goal of statistical validity and generalizability. When each member of the population has an equal probability of being included in the sample, it minimizes selection bias and helps ensure that the sample accurately reflects the diversity and characteristics of the whole population. This is essential for making reliable inferences from the sample data back to the broader population.

In contrast to this correct understanding, the other options imply concepts that do not align with the principles of random sampling. For instance, if every participant had a different chance of being selected, it would lead to bias in the sample selection, which undermines the representativeness of the sample. Choosing only the most relevant individuals or representing only the majority of the population also contradicts the premise of randomness, as it may exclude important diversity and fail to capture the true nature of the population being studied. Thus, the importance of the predefined equality in selection probability is what solidifies the concept of a random sample.