Older Adults Who Experience Their Lives to Be Completed and No Longer Worth Living: A Systematic Mini-Review Into Used Terminology, Definitions, and Interpretations

In the Netherlands and in Belgium, a political debate emerged regarding the possibility of euthanasia and assisted suicide (EAS) for older adults who experience their lives as completed and no longer worth living, despite being relatively healthy. This mini-review aimed to (1) present an overview of the terms used to denote this phenomenon as well as their definitions and to (2) explore how the underlying experiences are interpreted by the study authors. A systematic search was performed in Web of Science, MEDLINE, PsycINFO, and CINAHL, yielding 35 articles meeting the selection criteria. We selected empirical, English-language articles published in peer-reviewed journals. Participants had to have a first-person experience of the phenomenon or be assessed for it, or have a third-person experience of the phenomenon. Results show that the terms tiredness of life (ToL) and weariness of life (WoL) were used most frequently, also in the broader literature on suicidal expressions across the life span. Many studies mentioned operational definitions or synonyms rather than theoretical definitions. Moreover, inside the EAS debate, the term ToL was more common, its definition incorporated death wishes, and it was regularly framed existentially. Outside of this debate, the phenomenon was generally considered as a part of suicidal ideation distinct from death wishes, and its experience was often associated with underlying psychopathology. We discuss the need to establish consensus definitions and conclude that only a multidimensional view may be suitable to capture the complex nature of the phenomenon.


INTRODUCTION
Old age is associated with numerous losses, such as of cognitive and physical abilities and social ties. Still, the majority of older adults maintains high levels of life satisfaction up to an advanced age (Gana et al., 2013), with reductions in wellbeing usually only being observed in the very last phase of life (i.e., terminal decline; Gerstorf et al., 2008). A number of older adults, however, appear to cope less well with the challenges of late life and start to lack a sense of meaning. They develop the feeling that their life is not worth living anymore, sometimes reporting an associated death wish. These experiences also seem to develop in the absence of severe physical and mental disorders (van Wijngaarden et al., 2015;Van Humbeeck et al., 2020).
Research into this phenomenon is still an emerging area. Different terms, such as completed life, tiredness of life (ToL), or life fatigue, have been used to denote the phenomenon, but the terms lack agreed-upon definitions as well an integration with other research areas. Additionally, the terminology is influenced by the political debate that emerged in the Netherlands and in Belgium, surrounding the possibility of euthanasia and assisted suicide (EAS) for older adults experiencing their life as not worth living anymore (e.g., Oosterom and van de Wier, 2020). For example, the term completed life is a literal translation of the Dutch term "voltooid leven, " which is central in the EAS debate in the Netherlands. Hence, to advance the knowledge on the phenomenon, the use of consistent and well-defined terms as well as an integration with the broader literature is needed.
This mini-review therefore has two main aims: First, we seek to present an overview of the terms that have been used in the empirical literature to describe the phenomenon that older adults experience their lives as completed and no longer worth living. We will present both definitions/descriptions of these terms and the contexts and populations they are associated with, thus not restricting our search to their use in late life populations. Second, we aim to explore how the underlying experiences are interpreted by study authors (e.g., as a normative experience, a pathological condition, an existential problem).
By taking a broad approach, we hope to gain insight into the extent to which the various terms describe the same or differing (severities of) underlying phenomena, in how far they reflect a different theoretical approach, and where terminological and theoretical overlap with other research areas might lie.

Search Strategy
We systematically searched four databases: MEDLINE, PsycINFO (both via Ovid), CINAHL (via EBSCO), and Web of Science core collections. Databases were searched from inception until 16-03-2021. 1 Keywords were completed life, tiredness of life, suffering from life, weariness of life, finished with life, life fatigue, and their variations (e.g., "tired of living"; based on van Wijngaarden, 2016; for the full search strings per database see OSF). In addition to the database search, we examined the reference lists of included articles as well as of related reviews that were identified through our search for further references. 1 More detailed information on the methodology can be found on the OSF page of the study: https://osf.io/c48j6/.

Study Selection and Data Extraction
Articles were eligible if they (a) were written in English, (b) published in a peer-reviewed journal, (c) discussed the topic of "tiredness of life" (or an alternative term), (d) used an empirical study design, and (e) investigated either participants with a personal, first-person experience of the phenomenon or assessed them for this experience, or studied participants with a third-person experience of the phenomenon (such as caregivers). We focused on empirical English-language articles and a study population with experience with the phenomenon as we were interested in the international use of the terminology compared to the use within the national political debate.
Study selection was performed using Mendeley and Rayyan (Ouzzani et al., 2016). In the title/abstract screening, the first 50 references were screened independently by both authors, reaching an agreement of 98%. Consequently, the first author conducted the rest of the title/abstract screening as well as the full-text screening and data extraction. From all studies, we extracted general study details (first author, year of publication, country, and study design), study focus (main aims and results), terminology, definition/description/operationalization, and interpretation/framing. Depending on the type of sample studied, we also extracted information regarding participants' age and gender (first-person experience) or role/occupation and work experience (third-person experience). Doubts during screening and extraction were discussed with the second author.

Data Analysis
For the first aim, we made an overview of all (main) terms used for the phenomenon in the articles and then grouped them (e.g., combining tired of living and tiredness of life). For each of these terms, we then created an overview of the characteristics of the studies that applied a given term -namely country, publication year range, age range, type of sample, firstversus third-person perspective, and conducted inside versus outside EAS debate -as well as the definitions given. For the second aim, we assigned one or multiple primary and secondary perspectives to the articles based on the authors' explicit descriptions and interpretations as well as related phenomena and mentioned theories. We tried to stay as close as possible to the authors' wording. Then, similar to the first aim, we made an overview of study characteristics for every perspective.

Study Selection and Characteristics
The database search identified 533 records. After duplicate deletion, 299 records remained. Sixty full-texts were assessed for eligibility, leading to 35 studies being included in the synthesis. The reference list search did not identify any additional articles (for PRISMA flow chart see Supplementary Figure S1; Moher et al., 2009). An overview of the included articles is presented in Tables   Significant interaction between age groups and severity of suicidality, but increase especially marked in the more severe categories.

Quantitative
Investigate whether the wish to die or suicidal ideation is widespread among the elderly, and whether it is related to psychiatric morbidity.
The higher the intensity of the suicidality, the higher the probability that the person is suffering from a psychiatric disorder.   , and never used as main terms. We did, however, find some terminological overlap in a study that interpreted WoL in the light of a theory of caring sciences that proposes the existence of different kinds of suffering, one of which is termed "life suffering"/"suffering of life" [10]. Despite not specifying this term in our keywords, another synonym for ToL/WoL was "tedium vitae. " Tedium vitae was the major term in Ojabemi et al.
[12] and a synonym in Brunoni et al. [4], both studies conducted outside of the EAS debate.
In line with the previous finding, also the definitions/ descriptions of all employed terms revealed much similarity. In general, many studies mentioned synonyms or operational definitions or lacked any description at all, instead of providing a theoretical definition. Again, differences primarily emerged between studies that were conducted inside versus outside of the EAS debate. Outside of the EAS debate, most studies mentioned "the thought/feeling that life is not worth living" as their (theoretical) definition/description or operationalization/ measurement of the phenomenon [1;2;4;6-8;11-13;15-20].
Moreover, the majority of these studies regarded the phenomenon as a part of suicidal ideation with a low level of intent, independent of the specific term applied [1;3-4;6-8;11;13;15-20;22]. Interestingly, although these studies usually regarded death wishes as a more severe form of suicidal ideation in the suicidal process, some studies grouped ToL/WoL together with death wishes in their measurement or analysis [8;15-17;22]. Likewise, the supposed incremental relationship from ToL/WoL over death wishes to suicidal thoughts and attempts was found by some [1;17] but not all studies [16;18].
In studies conducted within the EAS debate, in contrast, the phenomenon was not explicitly linked to suicidal ideation. Multiple studies, sometimes considering WoL and life fatigue as synonyms, defined ToL as "suffering caused by the prospect of having to continue living with a very poor quality of life, not predominantly caused by a physical or psychiatric disease, and closely associated with (/leading to) a death wish" [25,29,[34][35]. One study additionally provided a definition of "completed life, " namely, "persons, mostly of old age, who do not see a future for themselves and, as a result, have developed a persistent, active death wish, without suffering that (mainly) originates in a medically classifiable condition" [25]. Usually, studies employing these definitions also mentioned the experience of feeling that "life is not worth living" in their further description of the phenomenon [25,27,[34][35]. Hence, definitions/descriptions provided by studies inside and outside the EAS debate partly overlapped. Within this debate, however, definitions of the phenomenon explicitly incorporated death wishes, though their exact role and severity remained unclear. Additionally, these definitions often specified the cause for the experience as at least partly situated outside of the medical domain.

How Is the Phenomenon Interpreted?
The majority of study authors adopted a psychopathological perspective [1][2][3][4][5][6][7][8][9][11][12][15][16][17][18][19][20][21][22][23], thus, for instance, viewing the phenomenon as a condition closely associated with psychiatric disorders and as requiring treatment. This perspective in many cases was the only interpretation given and was taken across countries and populations. Studies from the Netherlands and Belgium and concerning healthcare professionals or individuals requesting EAS formed an exception. Indeed, all studies adopting a psychopathological perspective were conducted outside of the EAS debate. The second most common way of framing the phenomenon was existential [10,13,24-25,27,29;31;34-35]. These studies related the phenomenon to a lack of meaning, experiences of emptiness, or difficulties with constructing a (cultural) identity. The existential perspective was predominantly found in studies from the Netherlands and from Belgium and thus within the EAS debate, though also two Scandinavian studies on young and old adults, respectively, adopted this perspective. Notably, the psychopathological and existential perspective never appeared in combination. Merely two studies with an existential perspective additionally discussed the phenomenon's possible relation to psychological (but not necessarily psychopathological) factors [13,34].
In addition, various studies interpreted the phenomenon as grounded in social/societal/cultural issues [4,9,13,25,27;32]   psychosocial problems [20,23,29,31]. These perspectives were always mentioned alongside other perspectives and were adopted independent of country and population, both inside and outside the EAS debate. Some ways of framing the phenomenon were exclusively found in studies linked to old age. These studies, for instance, stressed the importance of physical/medical aspects [23,25,[32][33], such as of fatigue and physical deterioration, or suggested an intertwinement with physiological aspects [23]. Moreover, a narrative perspective explaining the phenomenon as a potential consequence of perceiving one's life story as completed was adopted by two studies within the EAS debate [27,35]. Lastly, the hypothesis that life-weariness and death wishes are the result of rationally considering one's life situation was put forward as a (secondary) perspective [2,32]. Importantly, other studies explicitly questioned this interpretation [25,27]. Of note, we could not infer a perspective for four studies [14,26,28,30], mainly from inside the EAS debate and concerning end-of-life decision making. Therefore, these studies were not included in this part of the analysis.

DISCUSSION
Some of the terms used to denote the phenomenon that relatively healthy older adults experience their life as completed and not worth living are also employed in the broader empirical literature, Frontiers in Psychology | www.frontiersin.org especially on suicidal expressions across the life span. ToL and WoL are found most frequently, with many studies mentioning operational definitions or synonyms rather than theoretical definitions. Moreover, which terms are used, how these terms are defined, and how the experience is interpreted differs depending on country and whether a study is related to the EAS debate. Inside the EAS debate, the term ToL is common, its definition incorporates death wishes, and it is regularly framed as an existential problem. Outside of this debate, the term WoL is applied as well, the phenomenon is generally considered as a part of suicidal ideation distinct from death wishes, and its experience is often associated with psychopathology. These differences can be understood in the light of the criteria that have to be met to be eligible for EAS in the Netherlands and in Belgium, which specify that an individual's suffering must be grounded in a medical condition (De Jong and van Dijk, 2017). There is debate about whether older adults who do not suffer from a severe somatic or psychiatric disease but experience their lives to be completed and wish for death should have the option to request EAS (van Wijngaarden et al., 2017;Holzman, 2021). The definition of ToL inside the EAS debate is thus tailored towards this very specific group and is inherently inconsistent with a strictly psychopathological framing.
Despite their differences, the two lines of research on the phenomenon have similar limitations that future research needs to address. For instance, an overall lack of theoretical definitions and an inconsistency concerning the relationship between ToL/ WoL and death wishes was observed. Clarifying this question and establishing consensus definition(s) is not only crucial for comparability among studies but will simultaneously elucidate the appropriateness of viewing the phenomenon as a part of suicidal ideation. For example, while in suicide research advances have been made by distinguishing between suicidal ideation and suicide attempts (Klonsky et al., 2018), it is -especially for older adults -still unclear whether there are also qualitative differences within suicidal ideation (O'Riley et al., 2014;Van Orden and Conwell, 2016). Currently, age differences are difficult to determine, as inside the EAS debate the phenomenon is viewed as unique to late life, whereas outside this debate similar definitions are applied for varying age groups. It is conceivable, however, that reflecting about the worth of one's life and thinking about or even hoping for one's death can have different origins and meanings depending on an individual's life stage. In later life, it might be indicative both of normative developmental processes of dealing with mortality as well as of underlying suicidality (Van Orden and Conwell, 2016). One possibility to gain insight into these nuances is the adoption of more diverse study designs and of theory-derived research questions that move beyond investigations of prevalence, predictors, and end-of-life decisions. Indeed, the latter has been previously emphasized with regard to late-life suicide (Van Orden and Conwell, 2016).
At the same time, combining aspects from the two lines of research could deepen the current understanding of the phenomenon. For example, the idea that "life is (not) worth living" which was included in many descriptions of the phenomenon has also been conceptualized as an evaluative component of experienced meaning in life (Martela and Steger, 2016). Thus, incorporating an existential perspective more broadly outside the EAS debate seems warranted and might offer one theoretical route forward. Concurrently, even in the study on "completed life" that selected individuals without severe diseases, individuals with death wishes displayed poor mental health and sometimes reported the lifelong presence of their death wishes (Hartog et al., 2020). Therefore, also when studying seemingly healthy samples as often done inside the EAS debate, attention for (sub-clinical) psychopathology should be kept. Actually, the distinction between existential and psychopathological factors itself might be artificial given various accounts stressing their interplay (Yalom, 1980;Maxfield et al., 2014). Similarly, results point to social-relational as well as societal-cultural influences on the experience of the phenomenon. Introducing studies on the perspectives of caregivers and relatives also outside of the EAS debate could be one way to gain more insight into these dynamics.
The current findings are strengthened by the reviews' broad approach, including articles independent of, for example, their publication year, studied age group, or geographical location. Thereby, a comprehensive overview of research into the phenomenon was created which allows to discern variations as well as overlap in results depending on cultural developments and type of sample. At the same time, a limitation that should be kept in mind is that the findings on terminology are restricted by our keywords. There might be even more terms used to refer to the phenomenon, or related culture-specific phenomena.
Concluding, it is likely that only an integration of various perspectives will be able to do justice to the multidimensional nature of the phenomenon and can uncover potential variations in its experience across cultures, developmental stages, and health statuses. Ideally, this multidimensionality will also be reflected in the terminology used to denote the phenomenon(/a) -which is currently usually biased toward either a psychopathological or a political discourse, as well as in the applied measurement tools.

AUTHOR CONTRIBUTIONS
JA: conceptualization, data collection, data analysis, and writing -original draft. EW: conceptualization, data collection, data analysis, and writing -review and editing. All authors approved the final version of the manuscript.

FUNDING
This study was supported by the Research Foundation Flanders (FWO, Belgium; grant 1152421N to JA). The University for Humanistic Studies provided funds for open access publication fees. These funding sources had no role in the study design, collection, analysis, or interpretation of the data.