The above image is of an email that was sent to my University of Minnesota email address. It is for a research survey regarding tobacco use and exposure. The people conducting this research are using a combination of multiple sampling methods in order to gain data for their research. They also used some incentive in order to attract more participants.
Below I will lay out four sampling methods that were potentially used for finding participants in this survey:
This is a sampling method based on the convenience to the researcher. A researcher will find a sample that is easily accessible and choose them for their sample set. In this particular case, it was convenient for the researchers of the tobacco use survey to send this email out to a listserv containing all current students' email addresses.
The email that I received states that I was selected to participate in this survey via a random sample.
Random sampling is one of the most common methods of probability sampling. It could be implemented in a variety of ways including throwing dice, lotteries, drawing names from a hat, etc. In the case of this survey, I would assume that the random sampling was done via some form of random electronic selection among current University of Minnesota student email addresses.
This sampling method is based on the idea that a certain person or group of people will meet specific criteria that the researcher holds for their data collection. In this case, the researchers may be most interested in learning about the opinions of young, educated individuals regarding the topic of tobacco use and exposure. If this were the case, it was wise for them to have chosen students at a large university such as the University of Minnesota as their target sample.
This is a sampling method that relies solely on a peoples' willingness to participate. While some form of incentive may supplement this, it is based on the idea that the participant will not be compensated for their participation in the research. Also, it is not mandatory that these people participate at all; it is their own decision.
Volunteer sampling is used in this instance as the people who were selected to receive the invitation to participate in the survey are not required to do so and may only be inclined to do so based on their willingness to participate.
In addition to these sampling methods, I want to briefly touch on the incentive that was provided in order to get participants to take the survey. The email mentions that if a participant completes the survey, they will be eligible to win one of five $100 gift card to the University of Minnesota Bookstore. This is a great way to encourage voluntary participation in surveys, especially among young audiences like college students who are often looking for deals and extra spending money.