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illustrated in Figure 1.

Figure 1. Research model
Source: Authors
3. Methodology
This study employed a quantitative research design using a structured online
questionnaire to examine the proposed research model. The model integrates the
Extended Health Belief Model (eHBM) and Self - Determination Theory (SDT) to
investigate the impact of FOMO on Vietnamese Gen Z consumers’ intention to purchase
dietary supplements online.
The questionnaire consisted of two sections. The first section collected
demographic information (gender, age, education level, income, place of residence, and
online shopping frequency). The second section measured eight constructs: FOMO,
perceived susceptibility, perceived severity, perceived benefits, perceived barriers, self -
efficacy, cues to action, and purchase intention. Measurement items were adapted from
prior validated studies (Banerjee et al., 2025; Wang et al., 2024; Tedjakusuma et al., 2023;
Wang et al., 2022; Deshpande et al., 2014) and assessed using a five-point Likert scale (1 =
strongly disagree; 5 = strongly agree).
The target population was Vietnamese Gen Z (aged 19 - 28) who use social media
and have searched for or purchased dietary supplements online. Data were collected
through an online survey (Google Forms) using convenience sampling. After removing
incomplete responses, 399 valid questionnaires were retained for analysis.
Data were analyzed using Partial Least Squares Structural Equation Modeling (PLS -
SEM) with SmartPLS. The analysis followed a two - step approach: evaluation of the
measurement model (reliability and validity) and assessment of the structural model
using bootstrapping for hypothesis testing.
4. Research results
4.1. Sample characteristics
The final dataset comprised 399 valid responses. Female participants represented
78.5% of the sample, with the majority residing in Hanoi (67%). Most respondents
reported having a college or university education (90%). In terms of income, 35.6%
earned below 3 million VND per month, while 36.1% reported income between 3 and 5
million VND. Nearly half of the participants (49.5%) indicated monthly expenditures below

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