Which of the following sampling methods might use recommendations from participants to identify additional subjects?

Snowball sampling is characterized by the technique of utilizing existing study participants to recommend or recruit additional subjects. This method is particularly useful in studying populations that are hard to reach or where participants might not be easily identifiable or enumerated, such as in certain social or behavioral research contexts.

As participants are recruited, they provide referrals to others who may fit the criteria for the research, effectively creating a "snowball" effect as the sample size grows through these connections. This method leverages the networks and relationships within a population, making it a powerful tool when traditional sampling methods may not be as effective or feasible.

The other sampling methods mentioned, such as systematic random sampling, stratified random sampling, and simple random sampling, rely on more structured approaches where selection is based on randomization or predetermined criteria rather than the recommendations of current participants. These methods do not typically incorporate the snowballing recruitment strategy that characterizes snowball sampling.