Non-probability sampling method is used in this study. Non-probability sampling is a non-random selection which depends upon the biased view of the researcher. Therefore, it is impossible to calculate the probability of any objects included in a sample. This sampling method is preferred because it saves time and money compared to probability sampling.
It is easier to use and can be employed when the sample population is relatively small, as is the case of this study. Additionally, non-probability sampling uses More specifically, this study employs quota sample which is a type of non-probability sampling method often used in market research. The relevant factors such as gender, age range, and family size are controlled to ensure the groups in the sample are corresponding to the groups in the population.1. Following the criteria (quota and inclusion criteria), a set of 35 questions were sent to selected subjects who satisfy all requirements. The quota criteria are comprised of 3 factors: gender, family size, and city. At least 50% of the sample was women, 30% was single households, and nearly 80% of sample who grew up in developing cities in Vietnam.