The survey questions were originally written in English, and then translated into Vietnamese for Vietnamese people to easier understand the nature of the questions. The Oxford and Cambridge dictionaries were used in translating process to ensure both version have the same meaning. Furthermore, to ensure the best clarity of the questionnaire, a pilot interview was conducted with five respondents to guarantee the comprehension, layout, and structure of the questionnaire.
The questionnaire is comprised of five sections. In the section one (questions 1-7), the first three (1-3) based on the the inclusion criteria to ensure the participants are qualified. The next three (4-7) ones are demographic questions to meet the quote sample standard. The seventh question is a demographic one which is irrelevant to quota sample.
Questions 8-10 (section 2) measured the Product Category Involvement Scale built by Mittal. In the pre-test, this scale was used to choose the two objects (washing powder, perfume). There were 15 participants in the pre-test. In order to reconfirm the level of consumer involvement, this scale was included in the last section of the survey.
Question 11-18 (section 3) appraised the degree of brand loyalty of interviewees towards the selected products. Although, according to Yoo et al, this scale ensures the overall commitment of being loyal to a brand, a Cronbach’s alpha test was still conducted. Cronbach’s alpha test is used when we have multiple Likert questions in the questionnaire which constructs a scale and we want to measure the internal consistency reliability, which is the case of this study. Simply put, the reliability is the level of consistency of any given measurement of a concept or a set of scale, and Cronbach alpha test is a common way to measure that1. Originally, the scale was constructed from five indicators, but two indicators were not qualified to meet the standard of Cronbach’s alpha test. That is, they were not internally consistent with all other items. Therefore, refining the indicators to increase reliability of the study was required: those two indicators which did not reach the acceptable level of 0.7 were rejected. The maximum score of brand loyalty is 30 and minimum is 6. In section 3, questions 11-12 required interviewees to state two brands which they purchased the chosen products. Questions 11-18 consisted of two sets of three questions for two products. 5-point Likert-type scales was used in which 1 means strongly disagree, 5 means strongly agree.