Loneliness in Young Adulthood: a Protocol for a
Scoping Review of the Quantitative and Qualitative
Emma Kirwan ( email@example.com )
University of Limerick https://orcid.org/0000-0001-8536-023X
Páraic S Ó’Súilleabháin
University of Limerick
Institute of Public Health in Ireland
University of Limerick
University of Limerick
University of Limerick
Keywords: Loneliness, young adulthood, mental health, emerging adulthood, scoping review
License: This work is licensed under a Creative Commons Attribution 4.0 International License.
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Loneliness refers to the distressing feeling that accompanies the experience of perceiving the quantity or
quality of one’s social relationships as inadequate (1). There is increasing recognition of the prevalence
of loneliness in young adults. Despite this, there is no existing scoping review on loneliness in young
adulthood. Young adults (18-25 years) are in a critical life stage involving diverse social, demographic,
biological and cognitive transitions which may affect the development of loneliness. Evidence that
loneliness is a risk factor for poorer mental and physical health further emphasises the need to
understand the experience in this age group. Therefore, the aim of our scoping review is to provide a
summary of the quantitative and qualitative literature on loneliness in young adulthood.
The proposed scoping review will follow the Joanna Briggs Institute methodology and Arksey and
O’Malley’s (2005) framework for scoping reviews. Peer-reviewed journal articles and grey literature in the
form of reports or dicult-to-locate studies will be identied by: (a) electronic database searching, (b)
contacting national and international researchers in the eld, and (c) by posting general requests for
relevant information on Twitter. We will include all study designs published in English from 2000 to 2021
where loneliness (dened as subjective) is a key focus of the work and the mean age of participants is ≥
18 and ≤ 25 years. Editorials, commentaries, opinion pieces, dissertations, and book chapters will be
excluded. Articles will be selected for inclusion following screening of titles/abstracts succeeded by full-
text screening. Results will be presented in a narrative form to provide a descriptive summary of the
literature on loneliness in young adults.
The results of this scoping review will provide an up-to-date overview of available research related to
loneliness in young adults and will inform our future research in the area. Results will be shared through a
peer-reviewed journal publication and conference presentations.
This protocol is registered with the Open Science Framework (OSF) available at: https://osf.io/jfcmp.
Loneliness has been dened as the distressing feeling that accompanies the experience of perceiving
one’s social relationships as inadequate, either quantitatively or qualitatively (1). Although loneliness is
often viewed as a problem of older adulthood, the need to belong and maintain social connections with
others is observed across the lifespan and all age groups are susceptible to loneliness when these needs
are not satised (2, 3). In fact, loneliness is particularly prevalent in young adults; about 40% of young
adults (16-24 years) report feeling lonely often or very often (4). Despite its prevalence, loneliness has
only recently been recognised as an important issue in young adult groups and to our knowledge, there is
no existing scoping review on the topic.
Young adults are of particular interest in loneliness research considering that this life stage which marks
the transition from adolescence to adulthood is characterised by important developmental milestones,
cognitive and physical maturation, identity exploration, and increased autonomy which may place this
age group at increased risk for loneliness (5-7). While short-term, or transient, loneliness is unlikely to
have long-lasting consequences and might even function to motivate connection with others (5, 8, 9),
almost one in ten (9%) young adults will experience persistent loneliness (10). Individuals who suffer
from persistent, or chronic, loneliness tend to experience more long-term psychosocial problems and
negative health outcomes, relative to those with short term loneliness (9).
The prevalence of loneliness in young adults is concerning considering that the experience is a well-
established risk factor for poorer physical and mental health (8, 11). Lonely young adults are more likely
to experience depressive symptoms, to have poorer sleep quality, poorer self-rated general health, and
altered cortisol activity (12-15). Although the long-term health consequences of loneliness may not
become apparent until later life, the negative experience and behaviours associated with loneliness may
increase an individual’s risk early in life. Young adults who experience loneliness are more likely to
engage in health risk behaviours, to use negative stress coping strategies, and to have increased risk of
disability and lower income in midlife (16, 17).
Recognising that loneliness may have negative implications for young adults’ health emphasises the
need to consider the factors associated with loneliness in this group. Young adults have a similar, if not
higher, prevalence of loneliness compared to older adults (10, 18); however, research has tended to focus
on the latter. Although loneliness is a universal experience at the individual level, the risk factors
associated with loneliness and the inuence of these factors can vary across the lifespan. For example,
the association between loneliness and less contact with friends is strongest for young adults (19-34
years) compared to early (35-49 years) and late (50-65 years) middle-aged adults (19). Therefore, there is
a need for a greater understanding of the specic risk factors for loneliness in young adulthood and the
target groups for intervention, beyond those already identied (20).
Given its complex nature, it is unsurprising that research on loneliness spans many disciplines using
different theoretical perspectives; some approaches are specic to loneliness, but broader theories have
also been applied in this area. A leading approach is the cognitive discrepancy model (2), which
emphasises the role of individual traits and cognitive processes in the subjective experience of loneliness.
In contrast, the social needs approach (21) views loneliness as a multidimensional construct capturing
an unmet need for intimate attachment (emotional loneliness) or meaningful friendships (social
loneliness). Loneliness has attracted interest from sociologists, who have described loneliness as a
product of wider society (22). Other approaches relevant in loneliness research relate to social
connectedness, such as Bowlby’s (23) attachment theory which highlights the inuence of early
attachments on future psychological well-being. Finally, broader developmental approaches, such as
Bronfenbrenner’s (24) model of ecological systems, have demonstrated usefulness in loneliness research
(25). Theoretical approaches applied in loneliness research are not mutually exclusive and may overlap.
Therefore, the research on loneliness in young adults is likely to be somewhat disparate; yet no review of
loneliness in young adults has specically considered the theoretical approaches employed in this area
Denition of loneliness and young adults
Throughout this review, we will use the term loneliness to refer to the distressing feeling that
accompanies the experience of perceiving one’s social relationships as inadequate, either quantitatively
or qualitatively (1). Across age groups, loneliness is subjective and is only weakly associated with
objective measures of contact with friends and family (18, 26). Loneliness is distinct from social
isolation, solitude, and living alone, such that these situations may not be unpleasant; adolescents’
perception of loneliness in comparison to aloneness suggests that loneliness is seen as aversive and
related to negative affect like sadness, whereas aloneness is not perceived negatively (27).
There is no dened threshold for transition from adolescence to adulthood. Due to social and economic
changes in contemporary societies, the process of achieving adulthood may continue for several years
until the mid-to-late twenties (28). Many of the traditional markers of adulthood, such as the age of rst
marriage, are now being achieved later in life than in previous years (29). This prolonged development
from adolescence to adulthood has been termed “extended adolescence” by some developmental
researchers (30). Others have described young, or “emerging”, adulthood as a distinct period of the life
course from age 18 to 25 years (6). Emerging adulthood is characterised by instability, possibilities,
identity exploration, self-focus, and feeling in-between (7), and represents a separate life stage marking
the transition from adolescence to adulthood involving a unique constellation of demographic, social,
and psychological correlates (31), which may have bearing on the development of loneliness. Because
the changes associated with the
from adolescence to adulthood may be particularly relevant to
the experience of loneliness, our review aims to focus on young or “emerging” adulthood.
Review aims and objectives
Despite increasing research interest in loneliness in young adults (16, 32, 33), our preliminary search of
the literature (PsycInfo and Scopus on 9th February 2021) revealed no existing scoping reviews on the
topic. Given the broad nature of this topic, a scoping review, rather than a systematic review, will
summarise the existing literature on loneliness in young adulthood. Scoping reviews are particularly
useful for disparate literature or topics with emerging evidence (34). Like systematic reviews, scoping
reviews use a methodologically rigorous process to nd and synthesise literature (35). Rather than follow
a highly focused research question, scoping reviews aim to identify all relevant literature in an area (36).
Therefore, conducting a scoping review is an iterative process which enables us to make (and document)
necessary changes to the search strategy to identify relevant studies. We hope to provide a foundation to
inform subsequent loneliness research in young adults ensuring that studies are based on the most up-to-
date knowledge in the area.
The aim of our scoping review is to provide an up-to-date summary of the qualitative and quantitative
literature on loneliness in young or “emerging” adulthood. Our main objectives are (a) to identify what
theoretical approaches are used in research on loneliness in young adulthood, (b) to summarise the
evidence examining the correlates of and risk factors for loneliness in young adulthood, (c) to summarise
how loneliness is conceptualised and measured in research in young adults, (d) to summarise the
evidence on sex-gender differences in loneliness in young adults, (e) to identify and summarise the young
adult groups that have been included in previous loneliness literature; in doing so, we may identify groups
of young adults that are currently underrepresented in this area of research.
We will conduct a scoping review to provide a descriptive summary of the available research on
loneliness in young adults. Our review will aggregate and articulate the ndings without formal analysis
of the quality of the available studies.
This review is informed by the Joanna Briggs Institute (JBI) framework for scoping reviews (37) and
Arksey and O’Malley’s (36) seminal work in scoping review methodology. This protocol follows the key
stages proposed by Arksey and O'Malley (36): (a) identify the research question, (b) search for relevant
studies, (c) select studies, (d) chart the data, (e) collate, summarise and report the results.
Identifying the research question
Considering the aim and objectives of our scoping review, the following research question has been
formulated: What is known from the available literature about loneliness in young adults? In addition,
several sub-questions which will inform data charting and the reporting of results. These are:
1. What theoretical approaches have been used in research on loneliness in young adults?
2. What correlates of and risk factors for loneliness have been studied in research on young adults ?
3. In what ways has loneliness been conceptualised and measured in research on young adults?
4. Are sex-differences in loneliness observed?
5. What young adult groups have been researched in previous loneliness literature?
Information sources and search strategy
The following electronic databases will be searched: Scopus, PubMed, PsycArticles, PsycInfo, Medline,
ScienceDirect, and Applied Social Sciences Index and Abstracts (ASSIA). The search will be limited to
papers published from 2000 to 2021. This year limit is proposed for two reasons. First, Arnett’s (6)
seminal paper on emerging adulthood was published in the year 2000; considering that this is a highly
cited paper, we expect to nd more peer-reviewed research on our target population after this year.
Second, this year limit is in line with our aim to provide an up-to-date summary of the research on
loneliness in young adults.
The search strategy includes combinations of keywords and terms related to our population group of
interest (young adults) and loneliness (Table 1). The search strategy will be adapted for each database
listed above (example attached in Additional File 1). Following JBI guidance on scoping review
methodology, a preliminary search of two databases (PsycInfo and Medline) will be carried out. The
search terms may be modied to ensure that the search strategy is comprehensive.
Keywords and search terms to be used in the
Young* adult* Lonel*
Youth* Subjective social isolation
Young pe* Perceived social isolation
Grey literature and manual searches
The term ‘grey literature’ is commonly understood to refer to electronic and print sources (e.g., reports,
working papers, dissertations) that are not controlled by commercial publishing organisations (38). Prior
to devising a search strategy for grey literature, we considered the benets and challenges of its inclusion
in scoping reviews.
Overall, including grey literature provides the opportunity to produce a more comprehensive and
timeliness picture of available evidence in an area. The emphasis on knowledge transfer in areas related
to mental health, such as loneliness research, means that the publication of research in a scientic
journal may not be the best way to ensure that ndings are communicated to those most interested in the
topic (e.g., youth mental health organisations, policy makers). It is likely that information relevant to
loneliness in young adulthood will be found in reports by organisations or government bodies interested
in youth mental health (e.g., Jigsaw, SpunOut.ie, National Youth Council of Ireland) and these sources
may not be retrieved in database searching.
Of course, there are limitations to grey literature searching. First, the time consuming and heterogeneous
nature of grey literature must be considered (39). Tricco (40) recounted the challenge in screening
approximately 5000 titles and abstracts to include grey literature in a scoping review. Given that abstracts
are not available for many grey literature documents, the full text of individual documents may need to be
reviewed in order to determine eligibility. Second, there is no gold-standard method to systematically
search for grey literature. Grey literature search strategies are better described as systematic rather than
replicable; even if our search is replicable, other researchers may not retrieve the same results on
replication. Previous review papers lack adequate descriptions of the search for and synthesis of results
from grey literature sources (39). As such, we aim to be explicit in our methodology by outlining our
considerations and including a level of detail in the nal scoping review paper that maximises the
transparency of our grey literature search.
A key aspect of our grey literature search is maximising search sensitivity while retrieving search results
that are feasible for screening. In line with this, we considered the use of search engines such as Google
to source grey literature. Although search engines are easily accessible, the low specicity and sensitivity
of this method, as well as the likelihood of nding documents already found elsewhere, reduces its
effectiveness. Google results are inuenced by geographical location, previous search history, and
popularity, meaning that the replicability and consistency of the search results may be compromised (41).
Having considered the importance of including grey literature, the advantages and disadvantages of
different strategies, and the current variability in approaches to grey literature, we have devised a
complementary search strategy which specically relates to sourcing grey literature documents in the
form of reports or dicult to locate studies relating to loneliness in young adults. We have chosen two
methods to source grey literature in our scoping review: (1) by contacting national and international
researchers in the eld via I-LINK (International Loneliness and Isolation NetworK), and (2) by posting
general requests for relevant information on Twitter and by mentioning relevant organisations
(‘@organisation’) in such tweets, as described in Adams et al. (38).
We will identify key experts in the area via I-LINK; these researchers will be contacted and asked to
nominate documents for inclusion in the review. By contacting other researchers in the area we may also
identify studies in progress or recently published studies that are not retrieved in database searches. We
will also post general requests targeting national and international organisations on the social media site
Twitter and ask that other users repost these tweets, so as to increase the potential viewers. A previous
review found this to be a more ecient process than email or professional press requests (38). We will
receive and consider documents for inclusion in the review up until the point of submission to a journal.
The reference lists of previous reviews and articles eligible for inclusion (from either the core search or the
complementary grey literature search) will be examined to locate additional relevant studies.
Identifying relevant studies
Conducting a scoping review is an iterative process (34, 37), meaning that some changes to the inclusion
and exclusion criteria may be necessary following trial study selection. Any deviations from this protocol
will be clearly detailed in the ‘Methods’ section of the nal scoping review paper.
a. Research where loneliness, dened as ‘subjective’ or ‘perceived social isolation’, is a key focus of the
work (determined by the inclusion of a relevant aim, objective, or research question related to
understanding loneliness) or if the study measures and reports ndings related to loneliness under a
broader concept, such as ‘psychological well-being’, ‘mental health’, or similar.
b. Qualitative, quantitative, mixed-methods, systematic reviews, meta-analyses, meta-syntheses
c. Mean age of participants is ≥ 18 and ≤ 25 years. Emerging adults share some characteristics with
the life stages of adolescence and adulthood; samples that overlap our operationalization of
emerging adulthood (e., ≥ 18 and ≤ 25 years) with a wider age range, but that report a mean age ≥
18 and ≤ 25 years will be included.
d. Studies which focus on loneliness in clinical or specic subpopulations, such as young adults with
Type 1 diabetes (42), will be eligible for inclusion but may be summarised separately to studies of
general or community samples in the results section of the review.
e. Research articles are not limited by setting or geographical location.
f. Articles published in English (that is the only language of the researchers).
g. Publications in the form of peer-reviewed articles or grey literature to include reports from relevant
NGOs (e.g., SpunOut.ie, Jigsaw), loneliness organisations (e.g., Campaign to End Loneliness) and
government bodies (e.g., National Youth Council of Ireland) or dicult to locate studies (i.e.,
empirical research which has only recently or not yet been published in a journal).
a. Articles not related to loneliness (such as those only focused on social isolation or living alone) or
articles where loneliness is not considered a key aspect (e.g., loneliness is only included as a control
b. Articles where the mean age of participants is < 18 or > 25 years, where the age of the population is
not clearly described, or studies with a wider age range where data for emerging adults (i.e., ≥ 18 and
≤ 25 years) cannot be extrapolated.
c. Editorials, commentaries, opinion pieces, dissertations, and book chapters.
d. Articles published in a language other than English.
Articles retrieved from the database searches will be added to EndNoteX9 (Clarivate Analytics) to manage
the references. The rst author (EK) will conduct database searching and removal of duplicates. Articles
will be screened in two phases. First, the titles and abstracts of all articles retrieved from the database
search, as well as reports and empirical studies located from additional sources, will be screened for
eligibility by EK. Fifty percent of the titles and abstracts will be independently screened by a second
reviewer (SS). Studies and reports that do not meet our initial inclusion criteria will be excluded. Second,
the full-text of the remaining articles that appear to full the inclusion criteria will be obtained and
examined for eligibility by EK. Fifty percent of the full-texts will be independently reviewed by SS. Studies
that do not meet the inclusion criteria at this stage will be excluded and the reason for exclusion noted.
Any disagreement between reviewers in decisions regarding the eligibility of studies will be resolved by a
third reviewer. Rayyan QCRI software will be used to manage study selection. The study selection
process, including reasons for exclusion, will be presented in a PRISMA ow diagram in the nal paper.
Data charting will be carried out for all papers by one reviewer (EK). A proportion of the eligible papers
(minimum of 10%) will also be assessed by SS for accuracy. The data charting form will be pre-piloted on
a random selection of articles to ensure all relevant information is extracted. Uncertainty regarding the
charting of results will be resolved through discussion, including a third author if necessary. The charting
table will include the following details:
a. Author(s) information.
b. Year of publication.
d. Article title.
a. Country of origin.
b. Study setting (e.g., community setting, online survey, university).
c. Quantitative, qualitative, mixed-methods, review.
d. Study design.
e. Sample size.
f. Age range and average age of sample.
g. Sample characteristics (i.e., ethnic groups, nationality, university or non-university sample).
h. Gender distribution.
Subject matter information.
a. Study aims and objectives.
b. If the study specically concerns loneliness during the Covid-19 pandemic.
c. Theoretical approach used: whether specic to loneliness (e.g., the cognitive discrepancy model (2),
social needs approach (21)), or a broader paradigm (e.g., ecological systems theory (24)).
d. Typology of loneliness: loneliness as unidimensional or multidimensional (e.g., Weiss (21) subtypes
of social and emotional loneliness).
e. Assessment or measurement of loneliness: which psychometric measures of loneliness were used?
Were indirect or direct measures used, or both? Were psychometric measures adapted (i.e., was the
wording of the psychometric measure adapted, was the assessment adapted to make it suitable for
an online survey?).
f. Sex-gender differences (if assessed in quantitative studies): are sex-gender differences reported for
overall loneliness or for subtypes? What is the
value and effect size?
g. Correlates and risk factors assessed (only in quantitative studies): what is the
value and strength
of the association?
h. Qualitative research approach: e.g., grounded theory, IPA (only in qualitative studies).
i. Key themes (only in qualitative studies).
j. Main ndings and conclusions.
Summarising of results
The reporting of results will be guided by the Preferred Reporting Items for Systematic reviews and Meta-
Analysis extension for Scoping Reviews (PRISMA-ScR) (43). A completed PRISMA-P checklist is included
as an additional le to this protocol (Additional File 2). The aim of our scoping review is to provide a
descriptive summary of the available evidence; the quality of the studies included will not be assessed.
All ndings will be included in a narrative review. Studies which report on clinical or specic sub-
populations, such as individuals with inammatory bowel disease (44) or young adults with Type 1
diabetes (42), may be summarised separately to studies which focus on community samples. The
reporting of our results will be guided by our research questions. The theoretical approaches used in
research on loneliness in young adults (RQ1), correlates of and risk factors for loneliness (RQ2), and the
means of conceptualising and measuring loneliness (RQ3) will be recorded in tables with accompanying
narrative summaries. We will identify commonalities across studies and collate the extracted data.
Observed sex differences (RQ4) and the young adult groups previously researched (RQ5) will be reported
using a narrative summary. Included grey literature reports will also be summarised in the narrative
review. The ndings from both kinds of literature will be combined to address our primary aim in
providing a summary of the quantitative and qualitative literature on loneliness in young adults.
This review aims to be the rst scoping review to provide a descriptive summary of the available literature
on loneliness in young, or “emerging”, adults. Specically, we aim to summarise: (a) the theoretical
approaches used in this area, (b) the risk factors associated with loneliness in this group, (c) the
conceptualisation and means of measuring loneliness in young adults, (d) the observed sex differences,
if any, in loneliness in young adults, and (e) the young adult groups that have been included in previous
Following the completion of our scoping review, results will be shared through a peer-reviewed publication
and conference presentations. This review forms part of a larger project which aims to identify the risk
factors for loneliness in young adulthood. The results of this scoping review will provide an up-to-date
overview of available research related to loneliness in young adults and will inform our future research in
The potential limitations to our scoping review include that older studies (published before the year 2000)
and documents that are not available in electronic databases or online may be missed. However, we
anticipate that the majority of relevant literature will be captured by our search strategies, including grey
JBI: Joanna Briggs Institute; ASSIA: Applied Social Sciences Index and Abstracts; I-LINK: International
Loneliness and Isolation Network; NGO: non-governmental organisation; EK: Emma Kirwan; SS: Sarah
Summerville; PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-analyses; IPA:
interpretative phenomenological analysis; PRISMA-ScR: Preferred Reporting Items for Systematic reviews
and Meta-Analysis extension for Scoping Reviews; PRISMA-P: Preferred Reporting Items for Systematic
reviews and Meta-Analysis Protocols; RQ: research question.
Ethics approval and consent to participate
Consent for publication
Availability of data and materials
The authors declare that they have no competing interests.
The study is supported by the Department of Psychology, University of Limerick. The funder did not play
any role in the development of this protocol.
EK is the guarantor of the study. EK, PSO, AB, and AMC were involved in the conception and design of the
study protocol. EK, PSO, AB, JMM, and AMC contributed to the drafting and revising of the protocol
manuscript. SS was involved in the planning of study selection and data charting. The nal manuscript
was approved by all authors.
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