Which of the following is a disadvantage of random sampling?

A large group size can complicate sampling is indeed relevant in the context of random sampling. When dealing with a large population, achieving a truly random sample can be logistically challenging. This complexity arises from the need to ensure that each member has an equal chance of being selected, which becomes increasingly difficult as the population size grows. Additionally, managing a larger sample may require more resources and time, potentially leading to difficulties in maintaining randomness and minimizing bias.

In contrast, the other options present characteristics that do not align with the nature of random sampling. Random sampling is designed to reduce bias, not increase it. It does not guarantee that all participants will agree to take part, as participation is voluntary, and it is generally more efficient due to the systematic approach it uses to select participants. Understanding that while random sampling is a robust method for minimizing bias, it does come with challenges in larger populations is crucial for effective research design.