Quota Sampling as an Alternative to Probability Sampling? An Experimental Study

In spite of the establishment of probability sampling methods since the 1930s, non-probability sampling methods have remained popular among many commercial and polling agents, and they have also survived the embarrassment from a few incorrect predictions in American presidential elections. The increase of costs and the decline of response rates for administering probability samples have led some survey researchers to search for a non-probability sampling method as an alternative to probability sampling. In this study we aim to test whether results from a quota sample, believed to be the non-probability sampling method that is the closest in representativeness to probability sampling, are statistically equivalent to those from a probability sample. Further, we pay special attention to the effects of the following two factors for understanding the difference between the two sampling methods: the survey's topic and the response rate. An experimental survey on social capital was conducted in a student society in Northeast England. The results suggest that the survey topic influences who responded and that the response rate was associated with the sample means as well. For these reasons, we do not think quota sampling should be taken as an acceptable alternative to probability sampling.