Context
This study will be conducted in universities participating in the EUniWell alliance [15], including University of Birmingham (The United Kingdom), University of Florence (Italy), Linnaeus University (Sweden), Nantes University (France), Semmelweis University (Hungary), and University of Murcia (Spain). Characteristics of each university are presented below (Table 1).
Table 1
University characteristics
| University of Birmingham* | University of Florence | Linnaeus University | Nantes university | Semmelweis University | University of Murcia |
Number of students | 36,933 | 53,612 | 33,000 | 43,000 | 14,024 | 31,015 |
Proportion of international students | 31% | 8% | 2% | 12% | 35% | 3% |
Number of staff | 9,053 | 4,399 | 2,100 | 4,500 | 2,095 | 3,839 |
Proportion of international staff | 24% | Unknown | Unknown | Unknown | Unknown | Unknown |
Location | Urban | Urban and surroundings | Urban and surroundings | Urban and surroundings | Urban | Urban and surroundings |
Number of campuses | 3 (Edgbaston, Selly Oak, and the Dubai campus overseas) | 7 | 2 (Växjö and Kalmar) | 7 (Nantes, Carquefou and 2 surrrounding cities, Saint-Nazaire, Roche/Yon) | The university does not have a campus. Instead, its faculties, departments, hospitals, clinics, libraries, sport and accommodation facilities are scattered throughout the capital city of Budapest | 5 |
Type of campus (city or campus-based) | Campus-based | Both city and campus-based | Campus-based | City and campus-based | City-based | Campus-based |
*all estimates exclude the students and the staff at the Dubai campus of the University of Birmingham |
Study design: Discrete choice experiment (DCE)
A DCE is a method for eliciting preferences for the attributes of a product or service. Using survey methodology, DCEs assess preferences by asking individuals to make choices or trade-offs between hypothetical options that differ according to their attributes. This method is based on the principle that people derive utility, i.e., wellbeing, for a product/service from its attributes, and that the choices revealed through a DCE enable inferences on the relative contribution of each attribute and level to the overall utility of a product or a service. DCEs are based on strong theoretical underpinning (random utility theory) and are currently seen as the gold standard for evaluating preferences [16]. The development of a DCE involves a series of steps including the identification of attributes and levels, experimental and instrument design, data collection, and statistical analysis [17].
The overview of the study steps to develop the DCE is presented in Fig. 2 below, including a systematic literature review to identify the initial list of attributes and levels, focus group discussion using the nominal group technique approach to validate the list of attributes and levels, and think-aloud interviews to pilot test the survey.
Figure 1. Steps to develop the discrete choice experiment survey
Identification of attributes and levels
To identify potentially relevant attributes and attribute levels, we conducted a systematic literature review of preference-based studies focused on the drivers of meal choices [18]. The objectives of the review were to summarise the evidence generated from DCEs and other preference-based methods to understand meal-choice; and to identify a list of attributes for the development of a DCE to investigate demand for lunch on campus. We constructed a comprehensive search strategy and searched Web of Science, Scopus, Medline, Embase, PsychINFO, EconLit, and CINAHL to identify eligible studies. After title/abstract and full-text screening, 33 studies were included in the review. The important constructs, in terms of attributes and their levels, were extracted from the identified studies. They were clustered into groups corresponding to similar themes (e.g. taste, price), and ranked in terms of frequency of being included in the identified DCEs as well as their relevance to the project setting. The clarity and mutual exclusivity of the attributes on the list were further discussed by the project team. This resulted in the initial list of nine potentially relevant attributes accompanied by descriptions and corresponding levels (Table 2).
Table 2
List of attributes, descriptions and levels generated from the literature
| Attribute | Description | Levels |
1 | Environmental impact | Negative impact of food production on the environment (e.g. CO2 emissions, water usage, animal welfare) | Low; moderate; high |
2 | Food origin | Origin of the ingredients | Locally sourced; imported; unknown |
3 | Healthiness | Meal that is good for your health | Healthy; neutral; unhealthy |
4 | Price | Price paid for food | Cheap; average; expensive |
5 | Time | How fast the food is to access (including walking to the food outlet and waiting for the meal to be prepared) | Fast; moderate; slow |
6 | Sensory properties of a meal | Appearance, smell, taste, texture, and colour of the meal | OK; good; very good |
7 | Familiarity | Familiarity with the food options available | Not very familiar; somewhat familiar; very familiar |
8 | Naturalness | The extent of processing during the food production process | Minimally processed; processed; ultra-processed |
9 | Serving size | Size of the portion | Small; average; big |
Validation of the list of attributes and levels
From this initial list, the final list of attributes accompanied by descriptions and levels were determined using the nominal group method in a focus group. This technique has frequently been used to select attributes for DCEs [19]. The original aim was to recruit one member of staff and one student from each participating university, however due to difficulties with recruitment and delays with obtaining ethics approvals, the final sample for the nominal group included eight participants from five out of the six participating universities.
The participants were presented the initial list displayed in Table 2 and asked to:
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Discuss the clarity and mutual exclusivity of the attributes.
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Discuss the clarity of the descriptions.
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Prioritise the attributes in terms of their importance when selecting a meal.
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Discuss the appropriateness of the levels.
The session was conducted online and led by a moderator (IP). During the session, the participants were asked to think about choosing what to eat for lunch on a typical day on campus, when they did not bring their own lunch. During the session, participants discussed the initial list of attributes presented in Table 2; as a result of this discussion some attributes were combined (e.g. healthiness and naturalness) and new attributes were introduced (e.g. variety of meal options available and environment in which a meal is consumed). Participants were asked to provide written consent prior to participation and received shopping vouchers (value of £25/€30)
In accordance with good practices, we aimed to include a maximum of 6 attributes in the final list to avoid overburdening the DCE respondents [20]. Therefore, the focus group participants were asked to select the top-6 attributes they found most important when choosing lunch on campus. The results of the voting are presented in Table 3 below.
Table 3
Results of the attribute prioritization
Order of importance based on individual voting | Attribute |
1st | Price of a meal |
2nd | Nutritional content of a meal |
3rd | Time it takes to walk to the outlet and wait for a meal to be served |
4th | Sensory properties of a meal |
5th | Variety of meal options available |
6th | Naturalness of the ingredients used to prepare a meal |
7th | Serving size of a meal |
8th | Environment in which a meal is consumed |
9th | Familiarity with a meal |
10th | Environmental impact of a meal |
Based on the focus group discussion and voting, and subsequent discussion amongst the project team, the final list of attributes, descriptions, and levels were developed (Table 4). It is important to note that even though the focus group participants placed variety of meal options in the top-6, it was excluded from the final list of attributes, because variety was an attribute describing a collection of meal offers, rather than the attributes of a single meal.
Table 4
Final list of attributes, descriptions and levels
Factor | Description | Level |
Nutritional content | How well a meal is able to meet your nutritional and dietary needs | Insufficient; neutral; sufficient |
Price | Price paid for a meal | 20% below average; average; 20% above average |
Time | How fast the food is to access (including walking to the food outlet and waiting for the meal to be prepared) | Fast; moderate; slow |
Sensory properties of a meal | Appearance, smell, taste, texture, and colour of a meal | Poor; OK; very good |
Naturalness | The extent of processing of the ingredients during the food production process | Minimally processed; processed; ultra-processed |
Meal size | Amount of food you receive in a meal | Small; medium; large |
Design of choice tasks
The DCE choice tasks were designed based on the final list of attributes and corresponding levels displayed in Table 3 using dcreate package in Stata version 17.0 (StataCorp LLC, College Station, TX). This package allows for the development of an efficient design that maximizes the precision of estimates by using a-priori information on the levels for each attribute that were generated from the nominal group discussion. In line with good practice, we generated 3 blocks of 8 choice tasks. Furthermore, we included a test-retest validity question, a question that repeats twice in each choice, to test the consistency of respondents’ preferences. The test-retest validity questions are there as a validation check as if any respondent ‘fails’, they are excluded from further analysis. Within the DCE, each respondent will be randomly allocated to one of the three blocks of choice tasks. Choice scenarios will be presented using visual aids to ease comprehension. Figure 2 below shows an example choice task.
Figure 2. Example of a choice set in the discrete choice experiment
Survey design
The DCE will be incorporated within a larger survey that will also include questions about participants’ sociodemographic characteristics, food-related behaviour (e.g. typical source of lunch, usual diet, food allergies), opinions about food, experience of food insecurity, physical activity, and body composition. We will also assess the level of burden of survey completion. The original survey will be developed in the English language and translated into other languages (French, Swedish, Italian, Hungarian, and Spanish) by an external translation agency. Translations will be checked for correctness by the researchers (native speakers) in each participating university.
Pilot test of the DCE survey
Earlier versions of the survey were pilot tested with seven staff members and six students from the participating universities using a think-aloud interview approach. During these interviews we assessed the comprehensibility of the survey and the difficulty of completing it. Overall, participants found the survey understandable albeit rather lengthy and suggested some clarifications, for example, adding definitions to the listed diet types and eating patterns. It took them on average 15–20 minutes to complete. Based on the feedback from the pilot, we added clarifications and reduced the number of choice tasks from 12 to 8. All pilot participants signed consent forms and received a shopping voucher (value of £25/€30). The final version of the DCE survey is included in Supplementary File 1.
Data collection and sampling
To conduct the DCE survey, we will use QualtricsXM (Qualtrics, Provo, UT) for the respondents from all participating universities except for the Linnaeus University, for which the survey will be developed using Survey&Report (Artisan). The invitation to participate will be distributed to students and staff from the six participating universities using various media (e.g. university newsletters, flyers, directed emails, social media promotion, etc). In our study, we will aim to recruit at least 100 respondents from each category, i.e. 100 staff members and 100 students, from each participating university. This was sufficient according to the common rule-of-thumb estimation for DCEs [21].
Statistical analysis
The participant characteristics will be described using Stata software, version 17.0 [22]. Data on preferences will be analysed using Nlogit 6 [23]. Since all attribute levels are categorical, they will be coded using the effects-coding approach. For this analysis, one level of each attribute is omitted and non-omitted variables are assigned a value of 1 when they are present, and 0 when another non-omitted variable is present. In effects coding, non-omitted variables are assigned the value of -1, when an omitted variable is present. Effects coding yields a unique coefficient for each attribute level included in the study.
We will first analyse the choice data using a random parameter logit model that will capture preference heterogeneity. We will also estimate subgroup random parameter logit models to assess if the preferences varied as a function of participant characteristics (sociodemographic characteristics and health-related behaviours). Finally, we will estimate a latent class model to identify preference classes based on participants’ preferences. All participants who completed the DCE-part of the survey and passed the test-retest validity check will be included in the main analysis. Preference data from all participants regardless of the test-retest validity check will be analysed separately in a secondary analysis.
Ethics
Prior to their participation in the survey, all participants will be provided with clear information on the study aims and objectives and asked to provide consent. Participants will have the option to drop out of the survey at any point without providing a reason or facing consequences. Ethical approval for this study was sought from the university ethics committee in each participating university. This study was approved by the ethics committees of the University of Birmingham (ERN_1270-Jun2023), University of Murcia (M10/2023/046), Nantes University (n°031020230), University of Florence (n. 304 granted on 21/02/2024), and Swedish Ethical Review Authority (Dnr 2023-07604-01).