Study design
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 findings 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:
- What theoretical approaches have been used in research on loneliness in young adults?
- What predictors, outcomes, and risk factors for loneliness have been studied in research on young adults?
- In what ways has loneliness been conceptualised and measured in research on young adults?
- Are sex-differences in loneliness observed?
- What young adult groups have been researched in previous loneliness literature?
Information sources and search strategy
Electronic databases
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 find 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 modified to ensure that the search strategy is comprehensive.
Table 1
Keywords and search terms to be used in the database searches.
Population
|
Issue
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Young* adult*
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Lonel*
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Youth*
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Subjective social isolation
|
Young pe*
|
Perceived social isolation
|
Emerging adult*
|
|
Early adult*
|
|
Adolescen*
|
|
Teenage*
|
|
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 benefits 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 scientific journal may not be the best way to ensure that findings are communicated to those most interested in the topic (e.g., youth mental health organisations, policy makers). It is possible 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 final 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 specificity and sensitivity of this method, as well as the likelihood of finding documents already found elsewhere, reduces its effectiveness. Google results are influenced 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 specifically relates to sourcing grey literature documents in the form of reports or difficult 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 field 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 efficient 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. Also, we will identify organisations interested in youth mental health and loneliness (e.g., Jigsaw), and search their websites for relevant reports. 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 final scoping review paper.
Inclusion criteria
- Research where loneliness, defined as ‘subjective’ or ‘perceived social isolation’, is a key focus of the work (determined by the inclusion of a relevant aim, objective, research question, or hypothesis related to understanding loneliness, or if quantitative studies measure and report loneliness under a broader concept term, such as ‘psychological well-being’, ‘mental health’, or similar). Where it is difficult to determine if loneliness is a key focus of quantitative papers, we will employ the criteria that included papers must report analyses beyond the prevalence of loneliness. With regards to qualitative research, loneliness will be determined as a key focus of the work where papers discuss loneliness in the introduction of the paper.
- Qualitative, quantitative, mixed-methods, systematic reviews, meta-analyses, meta-syntheses articles.
- 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 (i.e., ≥ 18 and ≤ 25 years) with a wider age range, but that report a mean age ≥ 18 and ≤ 25 years will be included. Where studies are longitudinal in design, included studies must report loneliness for age ≥ 18 and ≤ 25 years.
- Studies which focus on loneliness in clinical or specific 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.
- Research articles are not limited by setting or geographical location.
- Articles published in English (that is the only language of the researchers).
- 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 difficult to locate studies (i.e., empirical research which has only recently or not yet been published in a journal).
Exclusion criteria
- Articles not related to loneliness (such as those only focused on concepts such as social isolation or living alone) or articles where loneliness is not considered a key aspect (e.g., loneliness is only included as a control variable and the study does not include a relevant aim, objective, research question, or hypothesis related to understanding loneliness).
- Articles where the mean age of participants is < 18 or > 25 years, where the mean 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.
- Loneliness scale development papers and literature reviews.
- Editorials, commentaries, opinion pieces, dissertations, and book chapters.
- Articles published in a language other than English.
Study selection
Articles retrieved from the database searches will be added to EndNoteX9 (Clarivate Analytics) to manage the references. The first 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. 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 fulfil the inclusion criteria will be obtained and examined for eligibility by EK. Fifty percent of the full-texts will be independently reviewed by a second reviewer. 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 flow diagram in the final paper.
Data charting
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 a second reviewer 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 including data extraction related to the research questions:
Bibliographic information.
(a) Author(s) information.
(b)Year of publication.
(c) Journal.
(d) Article title.
Key study and subject matter information.
(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) Study aims and objectives.
(g) If the study specifically concerns loneliness during the Covid-19 pandemic.
(h) Qualitative research approach: e.g., grounded theory, IPA (only in qualitative studies).
(i) Key themes (only in qualitative studies).
(j) Main findings and conclusions.
RQ1: What theoretical approaches have been used in research on loneliness in young adults?
(k) Theoretical approach used.
(l) If the theoretical approach is specific to loneliness (e.g., the cognitive discrepancy model (2), social needs approach (21)), or a broader paradigm (e.g., ecological systems theory (24)).
RQ2: What predictors, outcomes, and risk factors for loneliness have been studied in research on young adults?
(m) Predictors, outcomes, and/or risk factors for loneliness assessed (only in quantitative studies): p value and strength of the association.
RQ3: In what ways has loneliness been conceptualised and measured in research on young adults?
(n) Definition of loneliness used.
(o) Typology of loneliness: loneliness as unidimensional or multidimensional (e.g., Weiss (21) subtypes of social and emotional loneliness).
(p) 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?).
RQ4: Are sex-differences in loneliness observed?
(q) Sex-gender differences (if assessed in quantitative studies): p value and effect size. If sex-gender differences are reported for overall loneliness or for subtypes.
RQ5: What young adult groups have been researched in previous loneliness literature?
(a) Age range and average age of sample.
(b) Sample characteristics (i.e., ethnic groups, nationality, university or non-university sample).
(c) Gender distribution.
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 file 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 findings will be included in a narrative review. Studies which report on clinical or specific sub-populations, such as individuals with inflammatory bowel disease (44) or young adults with Type 1 diabetes (42), may be summarised separately to studies which focus on community samples. Please see the table outlining data charting and the anticipated results format in Additional File 3.
The reporting of our results will be guided by our research questions. The theoretical approaches used in research on loneliness in young adults (RQ1) and the means of conceptualising and measuring loneliness (RQ3) will be recorded in tables with accompanying narrative summaries. The predictors, outcomes, and risk factors for loneliness (RQ2) and observed sex-gender differences (RQ4) in loneliness in young adults will be recorded in tables reporting the p value and effect size. 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 findings 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.