School meal programmes subsidised by the US Department of Agriculture (USDA) are a crucial component of federal programmes addressing basic needs in the USA, helping to reduce food insecurity in low-income families(Reference Ralston, Treen and Coleman-Jensen1) and providing nutritionally balanced lunches and breakfasts to millions of students each year(2,Reference Au, Rosen and Fenton3) . Studies have shown that school meals in the USA provide better nutrient quality compared to meals from other sources, including those packed at home(Reference Vernarelli and O’Brien4,Reference Liu, Micha and Li5) . Correspondingly, students who participate in US school meal programmes consume healthier diets, including more fruits, vegetables and whole grains, than those who do not(Reference Au, Rosen and Fenton3,Reference Clark and Fox6) . These dietary improvements may be particularly important for improving health equity as the majority of children who participate in school meal programmes are from low-income households who qualify for free or reduced-price meals(Reference Billings7) and may be at increased risk for diet-related diseases(Reference Brady, Kohler and Zheng8).
The COVID-19 pandemic highlighted the significant impact of school meal programmes on students’ access to healthy foods and household food security. When schools across the USA closed due to the pandemic, millions of students suddenly lost access to school meals, putting them at risk of food insecurity(Reference Niles, Beavers and Clay9). In the face of this unprecedented event, the USDA issued a series of waivers allowing all students to access school meals at no cost, regardless of income. This was a departure from the typical models used in the USA, which include a three-tier payment model and the option for eligible schools to participate in the Community Eligibility Provision (CEP). In the three-tiered payment model, families either (1) submit income applications each year to determine student eligibility for free, reduced-price, or paid meals or (2) students can be directly certified without an application based on their enrolment in other federal assistance programmes(10). Under this system, families earning less than 130 % of the US federal poverty line (approximately $40 000 for a family of three, based on school year 2023–2024 estimates) or those who are directly certified qualify for free meals. Families earning between 131 and 185 % of the federal poverty line (up to about $54 000 for a family of four) qualify for reduced-price meals and pay $0·30 for breakfast and $0·40 for lunch. Lastly, families earning over 185 % of the federal poverty line pay a district set price, averaging $1·75 for breakfast and $3·00 for lunch nationally in 2024, amounts that are partially subsidised by the USDA and may not reflect the full cost of producing a meal. Alternatively, since its introduction as part of the Healthy, Hunger-Free Kids Act in 2010, CEP has enabled qualifying schools located in low-income areas to offer free meals to all students without collecting individual income applications. Prior to the COVID-19 pandemic, approximately 30 000 schools across the USA adopted CEP. By SY 23–24, participation in CEP grew to 47 766 schools(Reference Hyson and FitzSimons11), in part due to changes to eligibility requirements. However, despite this increase in CEP adoption, national data from the same school year show that 15 % of eligible schools did not participate in CEP(Reference Hyson and FitzSimons11), and non-participation rates were even higher in Arizona, with 48 % of eligible schools opting not to participate in the programme in SY 23–24(Reference Raval, Martinelli and Dykstra12).
While the nationwide pandemic-era waivers allowing free meals for all students were unprecedented in the USA, other countries have long adopted Universal Free Meal (UFM) programmes. Countries such as Sweden and Finland have had national UFM policies in place since the 1940s, while others like Brazil, Estonia, India and South Korea adopted national-level programmes more recently. Countries with well-established UFM policies like Sweden have provided evidence of long-term education, health and earning benefits for children with access to UFM(Reference Lundborg, Rooth and Alex-Petersen13). Similarly, school meals in Japan (while not universally free, but universally available and free for low-income students)(14) have also been associated with improved diet quality, especially in students from lower-income groups(Reference Kurotani, Shinsugi and Takimoto15). Despite widespread positive reactions to UFM policies in the USA among families(Reference Martinelli, Melnick and Acciai16) and success in other countries, the federal waivers allowing for free school meal distribution across the country ended at the end of the 2021–22 school year. Although a few states continued UFM(17), most reverted to the three-tiered payment system and CEP option that was in place before the waivers were implemented. Coinciding with this shift, there has been a notable decline in school meal participation, with 1·2 million fewer children eating breakfast and 1·8 million fewer eating lunches in school year 2022–2023 compared to 2021–2022, when UFM waivers were in place(Reference FitzSimons and Hayes18).
At the same time, the food insecurity rate among Arizona’s children was 14 % compared to the national rate of 12·8 %(19). Local community groups, including parent-led coalitions and anti-hunger advocates, worried that ending UFM at the national level might further exacerbate this issue and, therefore, sought to explore options to maintain access to school meals in Arizona. As policymakers and school meal advocates seek to gain support for UFM not only in Arizona but in other states and across the globe(20), it is important to understand the perspectives of key school stakeholders following the transition from free meal policies back to a tiered payment system. This understanding will highlight some of the benefits of UFM and reveal challenges to address when considering such policies. The objective of this mixed-methods study was to examine the opinions and perspectives of school professionals, teachers, administrators and other school staff regarding UFM policies following their implementation and subsequent de-implementation in Arizona.
Methods
This study used a convergent parallel mixed-methods design to capture school personnel’s opinions about UFM in Arizona(Reference Creswell21). Specifically, we used a survey instrument that included both closed-ended questions and one open-ended question. This approach allowed us to capture overall response trends using quantitative methods, while also gaining deeper insights into staff opinions about UFM programmes through qualitative analysis of responses to the open-ended question.
Survey instrument
A thirty-two-item survey was developed to gather opinions and perspectives regarding UFM from school staff members and caregivers of students attending Arizona public schools. This manuscript focuses on data from respondents who self-identified as school staff. Data from students’ parents are presented elsewhere(Reference Martinelli, Melnick and Acciai16). School staff were asked to select the job title that best described their role from the following options: classroom teacher, cafeteria staff/manager, school/district administrator and other school/district support staff. Respondents answered questions about their views on school meals, their level of agreement with various statements related to school meals, their level of support for the federal policy that allowed free meals during the COVID-19 pandemic and for a potential future extension of such policy in the state of Arizona. Additionally, they provided demographic information (e.g. race and ethnicity, annual family income and education level) and their political leanings by answering, ‘In terms of your views on political issues, how would you describe yourself? (Very or somewhat conservative, middle of the road, very or somewhat liberal, or not sure)’. This question was included given the potential variation in support for UFM programmes across different political leanings(22). Finally, an open-ended item, ‘Please provide any additional thoughts, opinions, or experiences you may have about offering school meals at no charge to all Arizona students regardless of family income’, was included at the end of the survey. Survey questions were adapted from previously developed surveys used in similar studies in other states, which relied on questions from studies conducted by the USDA about school meals and as well as questions developed by the research team in partnership with nutrition/school policy advocacy organisations. Questions were pilot-tested with school nutrition professionals prior to survey implementation(23–Reference Zuercher, Cohen and Hecht27). The full set of survey questions and answer options are presented in Appendix A.
Data collection
The anonymous survey was open for completion between September and October 2022, following the conclusion of federal waivers that allowed all students to receive free meals without income applications. The survey was distributed via the Qualtrics (Qualtrics International Inc., Seattle, WA) online platform. Recruitment was conducted using multiple channels. First, the survey was distributed to a convenience sample of six large urban public school districts located in the two major metropolitan areas in Arizona, home to approximately 80 % of the state’s population. Distribution methods varied slightly according to district policies, with the most common distribution methods being emails to school community members and posts on school-managed social media platforms. To supplement distribution to specific school districts, the Arizona School Nutrition Association shared the survey link with its members via email, and the study team further extended the survey reach by sharing it on social media platforms (e.g. X (formerly Twitter), Instagram). Respondents consented to participation before answering survey questions and had the option to provide their email address at the end of the survey to enter a drawing for one of five $100 gift cards. The survey took an average of 13 min to complete. All procedures were approved by the Arizona State University Institutional Review Board (STUDY00016016).
A total of 5431 responses were collected. To ensure data quality and integrity, responses from locations that were outside of Arizona were identified using geographic information systems (GIS) software, based on the latitude and longitude data for each response provided by Qualtrics, and then removed. This was done to remove instances of bot completions (n 1534). Next, the median completion time was calculated, and surveys completed in less than half the median time were removed from the sample (n 212). Of the remaining 3685 respondents, 1255 self-identified as school staff and were included in quantitative descriptive analyses. Of these, 518 provided comments in the open-ended question and were also included in qualitative analyses (Figure 1).
Description of study sample.
Data analysis
Descriptive analyses (i.e. frequency distributions) were conducted for closed-ended questions using Stata software version 16 (StataCorp LLC). Responses to the open-ended questions asking respondents to provide additional thoughts, opinions or experiences regarding free school meals to all students were reviewed and analysed to develop thematic codes by two researchers trained in qualitative methods (SM and EMM). At the time of analysis, both researchers were experienced in conducting research focused on school food service and SM had experience in school food service as a school nutrition professional. To minimise interpretive bias, both authors actively worked to set aside pre-existing assumptions and perspectives during the analysis process.
Thematic analysis of responses was conducted using an iterative constant comparative methodology(Reference Nowell, Norris and White28). The lead author (SM) first reviewed a subset of responses and developed an initial codebook based on a priori categories, including (a) reasons to support UFM and (b) concerns about UFM. The two researchers then independently read and coded a selection of 5 % of total responses using the initial codes. After independent coding, they met to resolve discrepancies, discuss potential new codes needed to capture provided thoughts and finalise the codebook with names and definitions for agreed-upon codes. Using this refined codebook, both researchers independently coded an additional selection of fifty open-ended responses (approximately 10 % of total responses) and again met to discuss any discrepancies in assigned codes to confirm consistency in code application. The remaining 75 % of responses were reviewed and coded by one researcher. After all coding was completed, the team met to identify and define final themes based on applied codes.
Results
Sample characteristics
Among the 1255 survey respondents who identified as school staff, 449 were teachers, 84 were cafeteria staff/managers, 106 were school administrators and 616 were other school staff. As shown in Table 1, about half of the respondents were non-Hispanic White (52·1 %), and 37·5 % were Hispanic. Educational attainment varied, with approximately 25 % of the sample reporting some college education, 28·1 % holding a 4-year college degree and 40·2 % possessing a professional or advanced degree. Almost 20 % of respondents reported an annual income of less than $34 999, 34·7 % reported an income between $35 000 and $64 999, 26·6 % reported an income between $65 000 and $99 999 and 19·5 % reported an income of $100 000 or greater. Finally, most respondents reported their political affiliation as either ‘middle of the road’ (31·1 %) or ‘liberal’ (42·2 %), while 18·5 % reported their affiliation as ‘conservative’ and 8·3 % were ‘not sure’ of their political preferences. Most responses came from staff at public schools (95 %). Compared to the state, our sample had a similar proportion of respondents who identified as non-Hispanic White and Hispanic, with 53·4 % identifying as non-Hispanic White at the state level compared to 52·1 % in our sample and 31·6 % identifying as Hispanic at the state level compared to 37·5 % in our sample(29).
AZ school community perspectives survey sample demographics for teachers and other school staff (n 1225)
* AIAIN, American Indians and Alaska Natives.
Closed-ended survey question results
Table 2 presents a summary of key quantitative survey results. An overwhelming majority of school staff expressed support for free meals during the COVID-19 pandemic (93 %) and for continuing to offer free meals in Arizona in the future (88 %). The majority of respondents in this sample (70 %) selected UFM as the best approach for providing school meals in the future, followed by changing eligibility criteria to include more children (22 %). Respondents also highlighted several benefits of making school meals available at no charge to all students regardless of family income. Across all groups (teachers, cafeteria staff, school/district administrators and other school staff), the top two benefits cited were ‘reduces childhood hunger’ and ‘removes major cost for low-income families’. Cafeteria staff were specifically asked to reflect on the benefits and concerns of offering free meals to all students related to school meal programme implementation. Key benefits selected include increased food service revenues due to increased student participation (49 %) and less time tracking and collecting school meal debt (48 %), while key concerns included staffing challenges (30 %) and lack of time for staff training (27 %) (Figure 2). A comprehensive summary of the quantitative survey results is available in Appendix A.
Summary of key survey results by respondent group
Full question and responses can be found in the appendix.
Top benefits and concerns to Universal Free Meals selected by cafeteria staff.
Open-ended survey question results
Arizona school staff perceptions and opinions of UFM were classified into six overarching themes based on the thematic analysis of open-ended survey responses. These themes and relevant quotes are described below and reported in two tables; the first presents themes related to reasons to support UFM (Table 3), while the second presents themes related to concerns about UFM (Table 4). Each quote represents a unique respondent.
Identified themes related to reasons to support UFM reported by school staff in public schools in Arizona (n 518)
Identified themes related to concerns about UFM reported by school staff in public schools in Arizona (n 518)
Reported reasons to support Universal Free Meals
Reduces stigma
An identified theme raised by school staff was the feeling of embarrassment or shame experienced by students and families participating in school meals under the three-tiered system. For example, one teacher shared, ‘The stigma regarding being a child who receives free or reduced lunch is significant. It is important for no child to feel discriminated against for any reason in a public school’. School staff also expressed concern that the stigma of applying for free school meals extends to parents and may prevent families from applying even when needed: ‘Some families don’t apply for free meals because of pride but the child suffers. Others are embarrassed to get the lunch so go hungry’ (Other school staff). When waivers allowing all students to eat for free were in place, school staff felt that feelings of shame were reduced. Notably, quotes from school staff often addressed both the role of stigma in school meals and the role school meals play in meeting students’ basic needs.
Improves students’ well-being and readiness to learn
Another important theme was the role of school meals in improving students’ well-being, including meeting basic nutritional needs. For example, one teacher shared, ‘My students often would not eat either breakfast or lunch without this program (UFM) and it allows them to get their basic needs met so we can focus on academics’. School staff noted that UFM polices reduced student stress related to school meal debt, ‘During the period of time when food was free, you did not see the students stress while in the lines to see if they would walk away with food or not. They were happy! They were able to enjoy time with their classmates and the food they received’. (Teacher). School staff were also concerned with the impact access to school meals had on academic achievement, especially for their more at-risk students: ‘We serve a great many students who come from food insecure homes. We have definitely seen a spike in classroom behavior and inability to focus among our students since the end of the free lunch program’ (Teacher).
Streamlines school meal process
A key factor in school meal administration is collecting annual income applications from families and verifying student meal eligibility status at each meal. School staff acknowledged the reduced burden on staff when all students eat for free, for example, ‘Since offering free lunch to all students the outcomes have been positive. The time it saves lunch staff in not having to collect money or guilt children who do not have money’. The three-tiered system can create barriers for families to complete the application: ‘We have students not getting lunch because parents have not started or completed paperwork’, (Other school staff) making the implementation of UFM policies a benefit.
Reduces burden on teachers
A common theme among teachers was the reduced need for them to provide meals and snacks to hungry students. After the COVID-19 era waivers, teachers reported a growing need to provide snacks to students, for example, ‘Since the free lunch program has ended I have seen an increase in hungry students in school. I regularly buy food for hungry students in my room so they have something to eat’ (Teacher). At the same time, teachers reported frustration and challenges in carrying this extra responsibility: ‘Students often come to my class hungry as they cannot afford school lunch or home lunch. I, as a teacher, do not have the means to keep supplying snacks to them’ (Teacher).
Concerns about Universal Free Meals
Programme implementation challenges
The key concerns about UFM expressed by school staff were related to programme implementation challenges, including food quality, increased food and materials waste and insufficient time allocated for lunch periods. Concerns about food quality were mostly associated with a perceived overreliance on processed foods and high amounts of salt, sugar or fat: ‘Every student should have the opportunity to eat a decent meal. The meals though should be more appetizing than a frozen heated meal’ (Other school staff). Another common theme focused on both food and packaging waste associated with school meals and the potential increase in participation in those meals. For example, ‘I love the idea that every kid who comes to school gets a lunch, however, the major increase in plastic packaging for every item is incredibly wasteful. I also hate the styrofoam trays and all other packaging that can’t recycle’ (Other school staff). The length of the lunch period was also a concern, as many staff members felt students need more time to eat: ‘Schools also need to make sure kids have enough time to eat and not tell them they have to leave after a short period of time--especially young children’ (Teacher). Despite these logistical concerns, staff continued to support expanded access to school meals, as exemplified by this quote from a school staff member: ‘There are ways to combat food waste and logistical problems. None of these issues are reason to scrap the program before funding it again’ (Other school staff).
Unfair burden for taxpayers
Some school staff did express concerns about the cost of feeding all students: ‘I believe that children should not suffer because of lack of parental responsibility; however, I am not certain taxpayers should incur the burden that more affluent people can manage themselves’ (Teacher). At the same time, school staff who mentioned the taxpayer burden still supported changing income requirements so that more families could qualify for the programme: ‘Although I don’t believe all students should be provided free meals, I do think we can do better by reviewing and improving the qualification used to determine eligibility’ (Other school staff). Even when concerns over taxpayer cost were mentioned, there was a desire to increase access to school meals beyond the current three-tiered system.
Discussion
Using a mixed-method approach, this study examined the perceived benefits and concerns related to UFM policies from school employees in Arizona. Both open-ended and closed-ended responses indicated strong support for UFM policies among school staff. A variety of reasons to support UFM were provided, including reducing the stigma associated with income-based school meal access, improving students’ overall well-being and readiness to learn and alleviating the need for teachers to personally address students’ nutritional needs. Key concerns were primarily related to the implementation of school meal programmes and to the cost to taxpayers.
As described in a prior publication, Arizona parents who completed this same survey cited similar benefits and concerns of UFM as school staff(Reference Martinelli, Melnick and Acciai16). Most parents (97·4 % of the 2347 parents included in the analytical sample) supported UFM in AZ schools. Similar to school staff, the key benefits of UFM cited by parents were reduced stigma associated with participating in school meals and improved readiness to learn. Not surprisingly, additional benefits cited by parents that were not mentioned by school staff included reduced financial and application burdens and reduced stress for families. Parents’ concerns about UFM were also similar to those of the school staff, with both groups worried about programme implementation challenges, such as food quality and waste, and taxpayer burden.
One key finding from this study is the stress that school staff experience when they perceive students to be food-insecure. School staff and teachers reported buying food to keep in their classrooms and helping students to cover meal costs when UFM policies were not available. While staff and teachers felt compelled to provide this support to their students, some also mentioned feelings of resentment and financial burden. This is concerning given the comparatively high levels of burnout among teachers(Reference Marken and Agrawal30), as this additional burden may exacerbate feelings of overwhelm. Indeed, access to resources is a key factor in determining a teacher’s desire to leave the profession(Reference Russell, Prince and Tyrone31,Reference Saloviita and Pakarinen32) . In addition to the burden of feeding students, teachers also noted classroom challenges when students are hungry and are not prepared to learn. The connection between student hunger, behaviour issues and academic achievement is well documented(Reference John and Karen33,Reference Johnson and Markowitz34) . Recent findings highlight the positive impact of UFM on student behaviour and academic outcomes(Reference Cohen, Hecht and McLoughlin35–Reference Domina, Clark and Radsky38). For instance, students in schools that provided free meals to all had a lower probability of suspension(Reference Domina, Clark and Radsky38) and were more likely to have positive academic outcomes(Reference Gordanier, Ozturk and Williams36,Reference Bartfeld, Berger and Men39) . The potential spillover effects of UFM policies on teacher well-being may be an additional benefit of these policies.
Whereas in other countries, school mealtimes are considered an integral part of the school day, in the USA, meals are often perceived as a distraction from classroom instruction(Reference Gaddis and Robert40). This oftentimes results in school food programmes with short meal periods and, accordingly, chaotic lunchroom environments. The perception of mealtimes as a distraction from classroom instruction in the USA may contribute to key concerns reported by respondents, long lines and insufficient length of lunch periods. These concerns related to students not having enough time to eat echo findings from previous research conducted among school staff before the implementation of UFM waivers in the USA(Reference Asperin, Nettles and Carr41). Importantly, short lunch periods impact students’ overall nutrient consumption during lunch(Reference Cohen, Jahn and Richardson42,Reference Hildebrand, Ely and Betts43) and the shortened service times contribute to challenges with preparing and serving scratch-cooked meals. In contrast, countries like Japan integrate school meals into the wider school community, involving parents, teachers and students (in addition to the food service staff) in the design and delivery of meals. Students participate in serving and cleaning up after meals, and food is an important part of the curriculum(Reference Gaddis and Robert40). UFM policies may present a pathway to address these concerns by (a) fostering a more inclusive environment where all students have access to meals and (b) making space for school meals to be better integrated into the school day, which would likely include longer lunch periods. In addition to UFM polices, to more specifically address concerns over the time allotted for school meals, increased coordination between school administrators, who are responsible for setting school schedules and allotted times for lunch, and food service staff is warranted.
Despite the strong support for UFM policies, school staff members did express concerns about costs for taxpayers and meal programme implementation. State-level UFM programmes would, in fact, require significant investment of taxpayer funds, which may pose financial challenges for many states. For instance, the state of Colorado, an early adopter of UFM post-COVID-19, is currently facing a budget shortfall due to participation rates that were higher than projected(Reference Gonzales44). In Arizona, multiple cost estimates were developed in 2023 to explore options for expanding access to school meals(Reference Martinelli, Acciai and Melnick45). As a result, the state covered the reduced-price co-pay for qualifying families starting in January of 2023(46). However, this funding has yet to become a permanent part of the state budget. Staff members also had concerns related to high levels of food and packaging waste, and relatively low levels of freshly prepared foods. Concerns about food quality align with previous findings from studies conducted with parents of students(Reference Martinelli, Melnick and Acciai16,Reference Farris, Misyak and Duffey47,Reference Meier, Brady and Askelson48) .
While overall levels of support for the continuation of policies allowing all students to obtain meals at no cost were high, support was slightly lower among cafeteria staff. As evidence, 80 % of cafeteria staff supported continued policies to provide all students free meals, compared to close to 90 % among other school staff. It may be that cafeteria staff are more acutely attuned to logistical challenges related to school meal distribution, since these staff are responsible for school meal programme implementation. Concerns cited by cafeteria staff in the present study such as finding enough staff to successfully run the programme, limited time available to train staff and inadequate storage space to accommodate increased participation may all contribute to their slightly lower approval of expanded meal programmes. Similar concerns related to programme implementation were shared by cafeteria staff in California, leading up to the implementation of a permanent UFM policy in that state(Reference Zuercher, Cohen and Hecht27). One notable benefit of UFM programmes for cafeteria staff is the elimination of time-consuming paperwork required to determine school meal eligibility. This change can free up cafeteria staff time and resources and allow them to increase focus on other priorities such as staff training and meal quality concerns(49). Further, corresponding policies should include increased funding for staff salaries and training. Notably, voters in the US state of Colorado approved UFM initiative which included language allowing participating schools to receive additional funding to directly support staff wages(50). This and similar provisions that boost school cafeteria staff salaries and provide additional funding for staff training could address some of the logistical issues cited by respondents.
Strengths and limitations
This study summarises the views on UFM from a large sample of Arizona school staff, with more than 1200 responses. Respondents also came from various educational, political and economic backgrounds. In addition, the survey was fielded at a critical point, just after the end of the federal UFM programme and the readoption of the three-tiered system, making the recall of UFM period more salient for respondents. However, the school staff were largely recruited by email request from a research team member from a convenience sample of large public school districts in Arizona with whom the research team had established relationships and therefore may not necessarily represent the views of all school staff in the state. To help address this, we conducted additional recruitment through the School Nutrition Association network and via social media channels to broaden the sample scope. Still, the majority of responses came from school staff in urban areas within southwest Arizona. Therefore, the perspectives of school staff in less-represented areas, specifically rural and tribal areas in the state, may not be adequately represented in this manuscript. As with all survey research, those who chose to complete the survey might hold different opinions from those who did not.
Conclusion
These findings underscore the strong support for UFM policies shared among school staff in Arizona and highlight the important role that UFM can play for both students and staff. Understanding the views and opinions from key stakeholders on campus is critical to the ongoing discussion of expanding access to school meals in the USA and globally. While UFM policies were broadly favoured, schools and policymakers should also consider ways to address concerns expressed by school staff. Future research examining models of UFM programmes globally, as well as in those states in the USA that have maintained UFM after the pandemic, and how these programmes have impacted all relevant school stakeholders may provide important lessons for expanding UFM polices in other areas.
Supplementary material
For supplementary material accompanying this paper visit https://doi.org/10.1017/S1368980025101171
Acknowledgements
The authors would like to thank school community members across Arizona, who made this project possible by dedicating their time to sharing their thoughts and opinions in the survey. The authors would also like to thank Daquin Tong for her support in the geographical analysis of respondent locations.
Financial support
This research was funded by Arizona Food Bank Network with support from No Kid Hungry Arizona (a part of Share Our Strength). Grant number G10154-300.
Competing interests
There are no conflicts of interest.
Authorship
Conceptualisation: S.M., F.A., E.M.M. and P.O-V.; methodology: S.M. and E.M.M.; formal analysis: S.M. and E.M.M.; writing – original draft preparation: S.M. and E.M.M.; writing – review and editing: F.A., P.O.V. and A.S.T.; visualisation: S.M. and E.M.M.; funding acquisition: S.M., F.A., E.M.M. and P.O.V. All authors have read and agreed to the published version of the manuscript.
Ethics of human subject participation
This study was conducted according to the guidelines laid down in the Declaration of Helsinki, and all procedures involving research study participants were approved by the Institutional Review Board of Arizona State University (protocol code STUDY00016016, October 18, 2022). Written informed consent was obtained from all subjects.
Open access
