Non-probability sampling method is used in this study. Non-probability sampling is a sampling technique in which it is impossible to calculate the probability of any objects included in a sample. A main pros of non-probability sampling is that 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 non-random selection which depends upon the biased view of the researcher.
More specifically, this study employs quota sample which is a type of non-probability sampling method often used in market research. The groups (i.e. males and females) in the sample are corresponding to the groups in the population. That is, the relevant factors such as gender, age, and family size are controlled to ensure the proportion. This type of non-probability sampling is useful when relevant control characteristics, such as gender, age range and household size are detected to ensure that the sample represents the population1.
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.