Aim of the review

The primary aim of this review is to address the gaps in the current literature by narratively synthesising existing research examining associations between death anxiety and self-esteem. Where sufficient data are available, a meta-analysis will be conducted to ascertain an overall effect size of this association.

The proposed review will answer the following review questions:

1. In adult participants (populations), to what extent is self-esteem (exposure) associated with death anxiety (outcome)?
2. Do demographic factors, such as gender or age, moderate the relationship between death anxiety and self-esteem?

Objectives

1. The primary objective is to narratively synthesise existing research examining associations between death anxiety and self-esteem, and to test the strength of these associations using meta-analysis, where sufficient data are available.
2. The secondary objective, where sufficient data are available, is to examine whether demographic factors, such as gender and age, moderate the associations between death anxiety and self-esteem.

Methods and analysis

Adherence to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines shaped the development of this protocol [20,21]. The protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO; CRD42024591775). See supporting information for a completed PRISMA-Protocols checklist (S1 File).

Types of studies

In developing inclusion and exclusion criteria for this systematic review protocol, the acronym PECO (Population, Exposure, Comparisons, Outcome) was employed (Table 1). Inclusion will be exclusively limited to peer-reviewed quantitative studies, including cross-sectional, experimental, quasi-experimental and intervention studies. To ensure that valuable sources of relevant quantitative data are not ignored, mixed-methods studies that concentrate on quantitative associations between death anxiety and self-esteem will be included, and only their relevant quantitative data will be extracted. For a quantitative or mixed-methods study to merit inclusion, it must report an effect size representing at least one of the following: 1. a correlation between death anxiety and self-esteem; 2. an effect size representing changes in self-esteem between pre-mortality salience and post-mortality salience timepoints; 3. an effect size representing differences in post-mortality salience death-thought accessibility across participants with high and low self-esteem, or; 4. Data from a TMT-based experimental study where self-esteem is included either an independent, dependent or moderator variable.

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Table 1. Eligibility criteria for the systematic review and meta-analysis.

https://doi.org/10.1371/journal.pone.0346665.t001

Qualitative studies, policy briefs or reports, opinion papers, commentaries, editorials, news, theoretical papers, conference presentations, dissertations, literature reviews, systematic reviews and meta-analyses will be excluded. In an effort to reduce risk of language bias, no language restriction will be used in determining exclusion of records [22]. Should non-English language records be available in languages spoken by members of the research team (Italian, French, Spanish, Latvian), they will be translated by the respective team member. Otherwise, non-English language records will be translated using a digital translation tool to translate the record to English [22].

Types of participants

The review will include studies that recruit adult participants (aged 18 years and above (population), for whom measures of self-esteem (exposure) and death anxiety (outcome) are reported.

Patient and public involvement

Given that the current research examines previously published data, participants were not directly involved or recruited for this review, and patient and public involvement was not necessary.

Types of outcome measures

The primary outcome measures for this review will be death anxiety and self-esteem, each measured by a validated scale in adult participants (aged 18 and above). Studies will only be included if they include a measure of effect for an association between death anxiety and self-esteem. Correlational research will be included if a correlation coefficient denoting the association between death anxiety and self-esteem is reported. Experimental studies (i.e., mortality salience studies) will be included if they examine changes in self-esteem between pre-mortality salience and post-mortality salience timepoints, or if they examine differences in post-mortality salience death-thought accessibility across participants with high and low self-esteem. TMT-based experimental studies will also be included, so long as self-esteem is included in the study design as either an independent variable or moderator variable.

Measures of effect

It is likely that some variety in scores and outcomes identified will be present, given the diversity of measurement scales. Thus, the frequency and prevalence of measurement scales will be noted in the data extraction sheet. Means, standard deviations, effect sizes and p-values will be extracted as measures of effect.

Search method

The search strategy was developed by TC and MD, in consultation with the UCC Academic Librarian. A systematic search of six academic databases (MEDLINE; PsycINFO; PubMed; Web of Science; CINAHL and; EMBASE) will be conducted using the following search string: (“death anxi*” OR “thanatophobia” OR “fear* of death” OR “fear* about death” OR “dying anxi*” OR “death attitudes” OR “death anxiety” OR “terror management” OR “terror management theory” OR “mortality salience” OR “death thought accessibility”) AND (“self esteem” OR “self-esteem” OR “self worth” OR “self concept” OR “self evaluation*” OR “self attitude*” OR “self liking” OR “self competen*” OR “self perception*”). Titles and abstracts will be searched for the search string terms by TC.

In addition to searching six academic databases, Google Scholar will also be searched, given its utility in supplementing searches of academic databases, with recommendations stating that on the first 200–300 records is optimal, as most sources that appear after the 200^th record are, on average, grey literature [23]. Adhering with these recommendations, Google Scholar will also be searched using the search string, and the first 200 records will be retrieved and screened for eligibility. TC will conduct these searches in December 2025.

Study selection

Identified records will be independently screened by members of the research team (TC, SK, CF, RH, KB), first by title and abstract and then by full text, so that each record is screened by at least two authors at each stage. The screening process’ inter-rater reliability will be calculated using the kappa coefficient. A data sheet designed by TC will be used for the purpose of this study.

Data will be extracted using a data extraction sheet designed by TC for the purpose of the review. Five authors (TC, SK, CF, RH, KB) will independently extract relevant data, so that data from each record are extracted by at least two authors, with conflicts and discrepancies being resolved through discussion and consensus with AS and MM. A PRISMA flow diagram will document the screening process, including reasons for excluding records. Data extraction will be completed by the end of February 2026.

Data extraction process

The following data will be extracted from included papers:

• Authors and publication year
• Region
• Sample description
• Study setting
• Measurement tools for death anxiety and self-esteem
• Effect sizes (e.g., correlations, F-values, chi-square values), p-values, means and SDs

Missing data

If data or details pertaining to a study’s procedure are missing from the report, the relevant corresponding author/co-author will be contacted in an effort to retrieve them. Failing this, the data will be excluded from analysis, and this will be addressed in the review’s discussion section.

Risk of bias assessment

The quality of evidence and methodology of included studies will be assessed using the Joanna Briggs Institute Critical Appraisal Tools. The appropriate risk of bias tool (i.e., Checklist for Analytical Cross-Sectional Studies, Checklist for Quasi-Experimental Studies, Checklist for Randomised Control Trials) will be applied to assess each included record’s quality based on its study design. Quality assessment will be conducted for each record independently by TC, SK, CF, RH and KB so that each included record is assessed by at least two authors. Papers will be classified as being low, medium and high risk, depending on their rating for each criterion. Each author’s assessments will be compared, and an inter-rater reliability coefficient will be calculated using the kappa coefficient. Doubts and discrepancies between the team will be resolved through mutual deliberation and consensus between the research team, AS and MM. Failing to reach consensus, MM will resolve the discrepancy as senior author.

Data synthesis

A narrative synthesis will be conducted of the included papers examining associations between death anxiety and self-esteem, in accordance with Cochrane guidelines [24]. Sample characteristics will be described and measurement tools for both death anxiety and self-esteem will also be noted.

Meta-analysis

For studies that present correlations between death anxiety and self-esteem, meta-analysis will be conducted with the pooled results using the MAJOR extension for Jamovi. Should sufficient data be available, demographic variables, such as gender and age, and clinical population status (clinical vs. non-clinical populations) will be examined as potential moderators of the relationship. Gender will be evaluated using data as reported within the individual included studies for the purpose of this review.

For non-correlational studies, relevant effect sizes (e.g., F-values, t-test effect sizes, chi-square values) will be extracted and standardised to allow for their inclusion in meta-analysis. Outcomes will be transformed into standardised mean difference effect sizes (Cohen’s d) and meta-analysis will be conducted to assess the weighted standardised mean difference across studies using Cohen’s d and standard error values.

I² values will calculate the statistical heterogeneity between studies, with values <25% indicating low heterogeneity, values between 25–50% indicating moderate heterogeneity and values >50% indicating high heterogeneity. A random-effects model will be used for highly heterogeneous studies (>50%) and, where the level of heterogeneity is not significant, a fixed-effects model will be applied to perform data pooling. A forest plot will also be generated and visually inspected for heterogeneity. Variance in the position of each study’s confidence intervals may suggest high heterogeneity. Should high heterogeneity be observed, meta-regression will be run to examine if the effect size changes based on specific study characteristics and sub-group analysis will investigate whether these individual characteristics act as sources of heterogeneity.

Visual examination of the funnel plot, the trim and fill procedure [25] and Egger’s regression test will assess included studies’ publication bias. Publication bias may be indicated by asymmetry in the funnel plot or by a significant intercept (p < .05) in Egger’s regression test. The trim and fill procedure will allow for publication bias to be adjusted by identifying which studies contribute to funnel plot asymmetry in the funnel plot, removing them to recalculate a more symmetrical funnel plot and associated pooled effect size and by replacing the originally removed studies with imputed mirror counterparts to create an unbiased, symmetrical plot [25]. A revised estimated effect size will be reported using the trim and fill procedure, should publication bias be identified through these procedures.

Strengths and limitations of the study protocol

This review’s notable strength is its adherence to a PRISMA-compliant methodology, ensuring transparency, reproducibility, and efficiency. The Joanna Briggs Institute Checklist provides a standardised framework for assessing evidence quality and methodological rigour in this study. The allocation of tasks within the research team will enhance efficiency [26], in turn reducing redundancy in efforts within the research team. A further strength of this review is its inclusion of both correlational and experimental studies, facilitating the examination of associations between variables [27] and the identification of potential cause-and-effect relationships [28]. This will broaden the scope of evidence and enhance our understanding of the associations between death anxiety and self-esteem. The inclusion of non-English language articles is also a strength, as it will help to reduce language bias within the current review [22] and allow for an identification of the scope of potential cultural variability in research examining death anxiety and self-esteem. Additionally, the measurement of death anxiety and self-esteem may vary across studies, potentially limiting comparability and reducing the precision of meta-analytical conclusions. Further, the inclusion of cross-sectional studies in the current review will limit inferences around causality between death anxiety and self-esteem.

Implications of the study protocol

Though self-esteem is central to TMT, a lack of a systematic overview of the association between death anxiety and self-esteem has limited our understanding of this relationship. Systematically evaluating the relationship between death anxiety and self-esteem will also aid in systematically evaluating the validity of TMT.

The current study also holds clinical implications. Systematically evaluating whether a significant relationship exists between death anxiety and self-esteem may clarify the role of self-esteem in treating death anxiety. Should a significant negative relationship be found, the findings will inform the development of death anxiety interventions and may point to the use of self-esteem interventions, which would offer an alternative to already-validated death anxiety interventions such as CBT [12] and meaning-centred interventions [13]. While existing CBT-type interventions have been effective in reducing death anxiety specifically, self-esteem interventions may aid in bolstering individuals’ resilience against death anxiety, lowering their susceptibility to death anxiety and subsequent need for clinical intervention. Subject to data availability, examining whether demographic factors, such as gender and age, moderate the effect between death anxiety and self-esteem will allow for an identification as to who might particularly benefit from self-esteem interventions, in terms of death anxiety, and subsequently aid in promoting better global mental health.