Sampling, Internet

Types of Probability Samples

In situations in which probability samples are used, the score that occurs most frequently in the sample is the score that should occur most frequently in the population. There are several types of probability sampling methods that could be implemented on the Internet. The “purest” method for collecting a probability sample is simple random sampling. In a simple random sampling, every participant has an equal chance of being selected for the study. This is often done using a table of random numbers. On the Internet, that type of sampling is most applicable to large groups for which a sampling frame with e-mail addresses of all members of the population (census) can be assembled. A census is possible with large corporations, universities, or governments. The invitation to take a survey is always made via e-mail. For example, the Pew Research Center conducts Internet surveys of random samples of elite and special populations, where a list of the population exists and can be used to draw a random sample. E-mail invitations still remain the most effective method of survey distribution.

Another form of probability sampling is systematic sampling. Systematic sampling involves selecting a sample by determining the sample size needed from the population and selecting every nth person from the population for inclusion in the study. Systematic sampling online is possible using pop-up surveys or intercept surveys where every nth visitor is asked to complete a study. Customer satisfaction surveys are most often conducted like this. A disadvantage is that people who are more satisfied with a product or brand are more likely to participate in those online surveys, as well as those who are computer and Internet savvy. Pop-up surveys also often have a reputation of being intrusive.

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