The Will-to-Live Scale: Development, validation and significance for elderly people
Sara Carmel M.P.H., Ph.D.
Center for Multidisciplinary Research in Aging, and Department of Public Health, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
CORRESPONDING AUTHOR: Sara Carmel, Center for Multidisciplinary Research in Aging, Faculty of Health Sciences, Ben-Gurion University of the Negev, PO Box, 653, Beer-Sheva, 84105, Israel.
[email protected], Tel.: 972 8 6477428, 972 8 6460584, 972526839383, Fax: 972 8 6477635
Acknowledgement: This work was supported by the US–Israel Binational Science Foundation (Grant number - BSF2008312, 2010); The Abraham and Sonia Rochlin Foundation. The authors gratefully acknowledge this support. Thanks to Dr. Norm O'Rourke who assisted with statistical analyses.
Word count: 5005
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The Will-to-Live Scale: Development, validation and significance for elderly people Sara Carmel Aging & Mental Health Abstract Objectives: In old age, the will-to-live (WTL) is one of the most important indicators of subjective well-being (SWB). However, few studies to date have focused on WTL. In these studies, WTL has mainly been evaluated via indirect questions concerning factors that may influence peoples’ WTL, or by measures directed to patients with specific diseases. The current study describes the development and psychometric properties of a new WTL-Scale. Method: The five-item WTL-Scale was developed on the basis of previous qualitative and quantitative research, and was evaluated in a longitudinal study of a random sample of 868 adults, aged 75+. Results: Confirmatory Factor Analytic (CFA) models were computed showing that each of the five items contributed significantly to measurement of a single WTL latent factor. Goodness of fit statistics were in ideal parameters for these CFA models at each point of data collection. Moreover, temporal analyses indicated that the relative contribution to measurement for each item was equivalent across time, attesting to reliability of measurement and the construct validity of WTL measurement. Concurrent validity was supported by significant positive correlations between WTL and life-satisfaction, happiness, self-rated health, morale, self-rated aging, and as expected, by inverse associations of WTL with depression and loneliness.
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Conclusion: The results of these analyses indicate that the WTL-Scale is a valid and reliable instrument. Considering the importance of the WTL concept in late life, and the psychometric properties of the WTL-Scale, we recommend it for use in research and practice related to older adults’ SWB and end-of-life care. Key words: Will-to-Live Scale, subjective well-being, elderly, Confirmatory Factor Analysis, psychometric characteristics.
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Introduction Striving for continued existence is a basic instinct and a natural driving force of all living beings. For humans, this existential drive has a cognitive-emotional facet influenced by each person’s personality and socio-cultural environment. These two interwoven phases are expressed in the Will-to-Live (WTL) concept (Carmel, 2001a). According to previous studies, elderly people have the ability to assess the strength of both of these phases and willingly rank the strength of their WTL (Carmel, 2001a; 2011). Importance of the will-to live in later life The importance of the WTL derives from its diagnostic and prognostic values. The diagnostic value is presented in the repeated significant and positive associations found between the WTL and other well-established indicators of subjective well-being (SWB) such as health status (physical and mental), self-rated health, self-esteem, life-satisfaction, happiness, a sense of wellbeing, living with a partner, and economic status, as well as in the negative associations with depression, anxiety, fear of death, hopelessness, social isolation, and loss of dignity (Beadle et al., 2004; Carmel, 2001a; 2011; Chochinov, Tataryn, Clinch, & Dudgeon, 1999; Chochinov et al., 2005; Ellison, 1969; Hockley, 1993; Huohvanainen, Strandberg, Pitkälä, Karppinen, & Tilvis, 2012; Karppinen, Laakkonen, Strandberg, Tilvis, & Pitkälä, 2012; Lawton et al., 1999). However, these associations between the WTL and indicators of SWB, although statistically significant, are not very high, suggesting that a person's WTL is in itself an indicator of SWB which reflects additional unique aspects of SWB not depicted by other SWB indicators. The existential dimension of commitment to life is one of these unique aspects embedded in the WTL. This aspect is naturally and unconsciously addressed in daily life by people of all ages
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when supplying their basic needs such as food, clothing, shelter etc., for their continued physical survival, as well as their higher-level needs such as self-fulfillment for promoting or maintaining the meaningfulness of their lives. Usually, young people are not consciously occupied with their WTL. Self-awareness of one's WTL arises when people realize that they are approaching the end of their lives, which happens in old age when one is exposed to age-related losses in almost all areas of life, and/or when one is diagnosed with a life threatening disease. This premise is supported by findings of a number of studies: in a national study of 1138 Israelis aged 70 and older, the WTL was found to have an important contribution to end-of-life care decisions in severe illness conditions, in addition to past experience with a dying person, fear-of-death and fear-of-dying, while controlling for self-rated health, social support and sociodemographic characteristics (Carmel & Mutran, 1997). The importance of the WTL as a unique indicator of SWB especially in old age is also expressed in the mechanisms by which WTL influences longevity and other indicators of SWB among older people. For example, Levy, Slade, Kunkel, and Kasl (2002) found that the WTL partially mediates the relationship between self-perceptions of aging and longevity, and in another study the WTL was reported to have a moderating effect on elderly people's decline in life-satisfaction, which is common with proximity to death (Carmel, Shrira, & Shmotkin, 2013). The prognostic value of the WTL is expressed in two longitudinal studies conducted in two different countries, and by use of somewhat different measures (Carmel, Baron-Epel, & Shemi, 2007; Karppinen et al., 2012). In both studies, the WTL was found to be a significant predictor of long-term (over 7.5, and 10 years, respectively) survival of elderly people, even when controlling for other important predictors of mortality/survival such as age and self-rated health. The powerful effect of the WTL on short-term survival was demonstrated by Sinard’s 5
analysis (2001) showing that people were able to postpone their death for the opportunity to live into the 21st century. In spite of these specific and unique features of the WTL, compared to other basic indicators of SWB, the WTL has drawn little attention among social and medical scientists, possibly because it has been considered "a normative human desire and too obvious to warrant a lot of attention" (Lawton et al., 1999). However, in recent years, following empirical WTLrelated findings, some researchers have suggested that the WTL is a phenomenon deserving further research (Carmel, 2001;2011; Carmel, Granek, & Zamir, 2015; Chochinov et al., 2005; Damron-Rodriguz & Carmel, 2014; George, 2012; Sinard, 2001). Measures for evaluating the will-to-live Due to the scarcity of studies on the WTL, only a few tools with different features have been developed for evaluating it. Some researchers have studied similar concepts and developed compatible tools such as the Valuation of Life (VOL) -Scale that measures a subjective perspective of the valuation of one's life, and includes items referring to meaningfulness of life and self-efficacy, but does not directly evaluate WTL (Lawton et al., 1999). Another indirect measure based on a semantic differential of three adjectives referring to a person's life as "emptyfull," "hopeless-hopeful," and "worthless-worthy," was used by Levy and colleagues (Levy et al., 2002). Ellison (1969), who investigated alienation among steelworkers, also included in his WTL scale a number of indirect questions such as "You sometimes cannot help wondering whether anything is worthwhile anymore," which do not specifically focus on one’s wish to continue living. Tsevat and colleagues (1999) used a time trade-off module which evaluates the number of years people desire to live in good versus imperfect health. The use of such indirect
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questions has focused mainly on factors that affect peoples' WTL. Some researchers have developed scales for assessing the desire to live of patients with specific life-threatening diseases, which caused them to include items such as "I am going to beat this regardless" (Beadle et al., 2004). Indirect evaluations of people's WTL were also conducted by questions pertaining to preferences regarding the number of years people wish to live or prolong their lives in various hypothetical scenarios characterized by various physical and mental functioning, and socioenvironmental conditions (Carmel, 2001a; Lawton et al, 1999; Levy, Ashman & Dror, 2000). Thus, most of the scales presented in the literature for evaluating people's WTL were based on indirect questions, which focused on factors influencing people's WTL such as meaningfulness of life and illness conditions. Direct single questions for assessing the strength of the WTL have been used by a small number of researchers: Chochinov and colleagues (1999) asked terminally-ill cancer patients to rank their WTL on a self-report 100 mm visual analogue scale, with "complete WTL" and "no WTL" as the extremes. Carmel (2001a) in an Israeli study conducted in 1994 on Israelis aged 70+, used the general question "If you could describe your will to live on a scale of 0 to 5, would you say that it is: 5=very strong, 4=strong, 3=intermediate, 2=weak, 1=very weak, 0=no will to live." In the Finnish longitudinal study, Karppinen and colleagues (2012) used the question "How many years would you still wish to live?" The importance of the WTL as derived from the abovementioned findings and a review of the scales used led us to engage in a search for the best way to assess elderly peoples' WTL. Therefore, in addition to open interviews preceding construction of the questionnaire for a series of quantitative studies based on a single item (Carmel, 2001a; Carmel et al., 2007; Carmel & Mutran, 1997; Carmel et al., 2013), and the results of these studies, we used a qualitative study in 7
which we asked 25 elderly people to define their WTL. The participants found this to be a difficult task because they perceived the concept as self-explanatory. This caused them either to point out that every living human wants to continue living, and/or to digress from defining the WTL to offering explanations about the personal and social conditions upon which their WTL depends (Carmel et al., 2015). In addition, similar to our experience with previous studies, older people willingly and with no reservations responded to open and closed questions referring to their own WTL, contrary to thoughts expressed by hesitant researchers and interviewers before conducting WTL-related interviews.
Development of the WTL-Scale The responses received in open interviews preceding the 1994 study (Carmel & Mutran, 1997), and in the abovementioned qualitative study (Carmel et al., 2015) indicated that elderly people perceive the WTL as a basic existential phenomenon and clearly understand its meaning. However, differences among them exist in the relative effects of various factors on their WTL. While for some people, family relations are the most important factor in determining the strength of their WTL, for others it is their health or economic problems. Given this finding, and the participants' expressed willingness to be interviewed about the WTL, as well as our previous good experience with use of a single direct question for evaluating WTL in the elderly (Carmel, 2001a; Carmel et al., 2013), led to the conclusion that direct questions would be the most effective and reliable way to evaluate older persons' WTL. The development of the new scale was based on both our aim to cover by direct questions a wider scope of the personal perception of the WTL phenomenon than that based on a general single question, and on the classic measurement theory, which posits that although a single 8
global question is simple to use and acceptable in evaluations of subjective reactions rather than in evaluations of objective phenomena, multi-item measures - even if unidimensional - are "more stable, reliable and precise" (Bowling, 2005, p. 343). Based on open interviews with elderly people conducted before designing the 1994 study on end-of-life care (Carmel & Mutran, 1997), we developed a scale comprised of 5 straightforward questions with six-category Likert scales for responses. All of the questions refer to self-assessment of the strength of the WTL, including a general perception of one's WTL, its strength in comparison to that of similar others, and its short and long-term stability (Appendix 1). The question for self-assessment of one's general WTL included in this scale (item No. 4 – Appendix 1) was previously used in a number of studies (Carmel, 2001a; Carmel et al., 2007; Carmel et al., 2013). Considering the abovementioned advantages of the WTL concept and measure for research and practice, the purpose of this study was to present the 5-item WTL-Scale and to describe its development, latent structure, temporal consistency of the latent structure, internal reliability, and validation. Methods Sample and process From the records of Israel's Ministry for Internal Affairs, we randomly recruited people aged 75+, living in three cities in the north, center and south of Israel (in similar proportions). After obtaining ethics approval from the Research Ethics Board of the Ben-Gurion University of the Negev, we randomly selected by telephone interviews participants who were 75 years and older, independent in ADL, cognitively competent, and able to respond to questions in Hebrew or Russian (because of the high percent of old Russian immigrants since 1989). Altogether, 1,216 elderly persons were interviewed at baseline (T1). Two additional waves of interviews were 9
conducted with a one-year interval (T2 and T3, respectively). In the second wave, 1,019 (83.8%) of the original participants were interviewed, and 892 in the third wave (73.4% of the original sample and 87% of the T2 participants). After excluding 23 participants who did not respond to all of the questions included in this study, we were left at T3 with 868 participants (about 71% of the original sample). A comparison between participants who dropped out from the study at T1 and T2 (n=348) to the 868 who remained at T3 showed that those who dropped out had significantly lower scores on health and on all the studied indicators of SWB except for loneliness and WTL. All of the participants were interviewed in their homes by trained interviewers. The interviews were based on a structured questionnaire. The average age of our 868 participants was 83.9 years (SD=3.91), ranging from 78 to 99. Women comprised 46% of the sample, and 56.7% of the sample were married or living with a partner. Instruments The WTL-Scale – As presented above, the scale included 5 items with six possible responses on Likert scales (see Appendix 1). Subjective well-being measures: SWB was measured by eight different scales for evaluating cognitive and emotional dimensions and perceived health status: (1) The Philadelphia Geriatric Center Positive Morale Scale (Lawton, 1975), comprised of 17 items, with a 4-point response scale, and an index based on the average score of all responses; (2) The Life Satisfaction Index-A (Neugarten, Havighurst, & Tobin, 1961), with 20 items, a 5-point response scale and an index based on the average score; (3) The Satisfaction with Life Scale (Carmel, 2001b) based on the 10
average score of responses to the degree of satisfaction (on a 5-point scale) with: physical health, mental ability, relations with friends, relations with family, ability to help family and life in general. This scale was previously validated in other studies (Carmel, 2001b; Carmel & Bernstein, 2003); (4) Self-rated aging was evaluated by the average score of a 3-item scale developed for this study, e.g. "To what extent do you agree with the sentence - I am aging well” with a 10-point response scale; (5) Happiness was measured by the 4-item happiness scale developed by Lyubomirsky and Lepper (1999); (6) Geriatric Depression Scale (GDS) (Sheikh & Yesavage, 1986; Zalsman, Aizenberg, & Sigler, 1998), comprised of 15 items with “Yes” and “No” responses, and an index based on the sum of scores; (7) Loneliness was evaluated by a 4item scale (Hughes, Waite, Hawkley, & Cacioppo, 2004); (8) Self-rated health was assessed by a single question for perceived general health status with a 6-point scale (from "very bad" to "excellent"). Socio-demographic characteristics: This group of variables included age, gender, family status, self-rated economic status, and education level (assessed by completion of: 1. Elementary school, 2. High school, 3. Higher education, 4. Academic degree). Analytic procedures Confirmatory factor analytic (CFA) models were computed independently at each point of data collection. Each of the five WTL items was assumed to load significantly onto a higher-order WTL latent factor. Samples of 868 for each model were sufficient to provide statistic power estimated at .99 (O’Rourke & Hatcher, 2013). CFA models were computed with the AMOS 22.0 statistical program using the maximum likelihood method of parameter estimation. Invariance analyses comparing CFA models were next undertaken to compare the relative contribution to measurement of each WTL item at each point of measurement. This was done by 11
fixing corresponding items across models in succession. With each comparison, a statistically significant change in chi-square values indicates a significant between-group difference or differences. Invariance analyses were undertaken in accord with the procedures described by Byrne (2004). CFA and invariance analyses examine the latent structure of WTL, not scale response levels. By contrast, response levels can be the same across groups yet the latent structure of these responses may differ significantly (and commonly does); moreover, response levels may vary greatly between two samples across groups yet the latent structure of responses can be similar (e.g., O’Rourke, 2005). The psychometric structure of scale responses is believed to reflect the underlying construct or constructs being measured (Byrne & Campbell, 1999). Internal reliability of the 5-item scale was assessed by Chronbach's alpha, and validity by correlations between WTL and the other SWB constructs. The predictive power of the previously used single item in comparison to that of the 5items included in the new scale was evaluated by a hierarchical regression analysis on positive morale, with WTL items as independent variables. Results Each item contributed significantly to measurement of a higher-order will-to-live latent construct. As shown in Figure 1, standardized coefficients are large (.63 ≤ ß ≤ .86) and statistically significant at all three points of data collection (i.e., t > 6.31; p < .01). On average, item 2 (“Compared to others your age, how would you rate your will to live?”), and item 3 (“How would you rate your will to live today compared to when you were younger?) contributed most to the will to live latent construct followed by item 4 (“On a scale from 0 to 5, would you say your will to live is…?”). ___________________________
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Insert Figure 1 about here ____________________________ Goodness-of-fit statistics for CFA models are in ideal parameters at all three points. At Time 1, the Comparative Fit Index (CFI ≥ .95; CFI = .99), the Standardized Root Mean Square Residual (SRMR < .056; SRMR = .011), and the Root Mean Square Error of Approximation are each optimal (RMSEA < .056; RMSEA = .020; Hu & Bentler, 1999); also, the full 90% confidence limits for the RMSEA statistic are within ideal limits, 0 < RMSEA CL90 < .038. Similar findings emerged in analyses of Time 2 data (CFI = .99; SRMR = .012; RMSEA = .041, .006 < RMSEA CL90 < .074), and Time 3 (CFI = .99; SRMR = .009; RMSEA = .055, .026 < RMSEA CL90 < .078). Model fit was calculated after correcting for correlated error between items 1 and 4. Invariance analyses were then performed to examine the measurement properties of each item over time. This was done to assess the temporal consistency of item measurement. As shown in Table 1, there is no change in the chi-square statistic as items are equated across Times 1-3. Coefficients independently estimated at each point do not differ for any item, and the relative contribution to measurement of each WTL item is consistent over time, indicating temporal consistency. ___________________________ Insert Table 1 about here ____________________________ The average scores on the WTL-Scale were quite similar at the three points in time [3.57 (SD = .74), 3.54 (SD = .81), and 3.54 (SD = .93), respectively, F(df=2, 1700)=1.28, P=.28]. 13
Internal reliability as measured by Cronbach’s alpha was in ideal parameters at each point of data collection (α= .83, .86, .90, respectively). Validity of the WTL5 item scale was assessed by correlations with other well-established indicators of SWB, conducted on data collected at the three points of time. Concurrent validity of the scale was supported by the significant Pearson Correlation Coefficients found between the WTL scores and the scores on two different measures of life-satisfaction (.43 to .51), positive morale (.40 to .52), happiness (.45 to .48), self-rated aging (.43 to.46), self-rated health (.36 to .38), and as expected by the significant negative correlations between the WTL scores and depression (-.46 to -.55) and loneliness (-.28 to -.30). The same analyses were repeated with the formerly used single-item WTL measure (item No. 4 in the 5-item scale - Appendix 1). The resulting r-scores with life-satisfaction measures ranged from .38 to.45; with positive morale from .36 to .47; with happiness from .43 to .45; with self-rated aging from .39 to.43; with self-rated health from .32 to .34; with depression from -.42 to -.50, and with loneliness from -.30 to -.32. All of these associations were found to be in the expected directions and statistically significant, but all of them were systematically weaker than those found between the 5-item scale and the same constructs of SWB, except for the associations with loneliness. This systematic difference in scores indicates that in general, the 5item scale is more sensitive than the single-item measure to various aspects of SWB included in the other SWB constructs. In addition, for evaluating the additive value of the 5-item scale over the single-item measure to the prediction of SWB, a hierarchical regression analysis was performed on T3 positive morale by the baseline (T1) 5 items comprising the WTL new scale. In the first model, only the single item was included (item No. 4 in the 5-item scale). In the second model, the other 4 items of the scale were added. This resulted in a statistically significant 14
increase in R2 indicating that the 5-item model significantly improved the prediction of positive morale (p=.000). Discussion Repeated findings about the diagnostic and prognostic values of the WTL and its role in end-oflife care preferences have raised researchers' awareness to the importance of WTL in old age, and caused them to suggest promoting related research and implementing the WTL in practice (Carmel, 2001a, 2011; Carmel et al., 2015; Chochinov, et al., 1999; Chochinov, et al., 2005; Damron-Rodriguez, & Carmel, 2014; George, 2012; Karppinen, et al., 2012). These findings and suggestions led us to search for a practical and methodologically appropriate tool to evaluate older people's WTL. A literature review of the measures that have been used for evaluating the WTL, open interviews with older adults about end-of-life issues preceding a quantitative study (Carmel & Mutran, 1997), previous experience with using a single item in quantitative studies (Carmel, 2001), and results of a qualitative study in which older adults were asked to define their WTL, all guided us to develop a new scale. In this paper we describe the development of the WTL-Scale and its psychometric structure at three annual points of data collection. The WTL-Scale presented here is comprised of five straightforward questions referring to the strength and stability of one's WTL. As such, this scale differs from some of the previously used tools, most of which focus more on factors that can influence people's WTL such as meaningfulness of life, health conditions or social circumstances (Beadle et al., 2004; Ellison, 1969; Lawton et al, 1999; Levy, Ashman, & Dror, 2000; Levy et al., 2002; Tsevat et al., 1999), rather than referring directly to the strength of the WTL itself. Some studies used a single general and direct question. However, although the measure was found to be valid, and interesting
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findings were reported in previous studies in which a single global item for evaluating the WTL was used, according to the classic measurement theory, measures based on single items are at a relative disadvantage in comparison to multi-item scales which - even if unidimensional - are more sensitive to changes over time, more precise and reliable (Bowling, 2005). Considering this, the suggested WTL-Scale was constructed using five questions (a minimum for multi-item measurements – Bowling, 2005), all of which refer to the strength of one's WTL in the present, past (short and long-term), and in comparison to peers, as well as its stability over time. Our statistical analyses were conducted on data collected in face-to-face interviews with a random sample of people aged 75+, at three points of time with one-year intervals. Confirmatory factor analytic (CFA) models were computed at each point of data collection examining the psychometric properties of the five WTL Scale items. Goodness of fit statistics for CFA models were found to be in ideal parameters indicating a single WTL latent factor significantly measured by five items at each point of data collection. Invariance analyses compared CFA models to assess the temporal consistency of item responses over time. Results indicate a single WTL latent construct measured by five items, and that the psychometric properties of responses to each item are consistent across points of measurements. Internal reliability as measured by Cronbach’s alpha was in ideal parameters at all three point of time (α = .83, .86, & .90, respectively), similar to the levels reported in previous studies with older adults (Carmel, 2011). Validity of the WTL-scale was supported by the significant positive correlations in the expected direction which were found with six different indicators of SWB including: Positive morale (Lawton, 1975), two different life-satisfaction constructs, (Carmel, 2001b; Neugarten et al., 1961), happiness (Lyubomirsky & Lepper, 1999), self-rated aging, and self-rated health, as well as by the significant negative associations between WTL 16
scores and the scores on depression (Zalsman et al., 1998) and loneliness (Hughes et al., 2004). These results were consistent in analyses of data collected over the three consecutive years. The advantage of using the 5-item WTL-Scale over the single-item measure was demonstrated by the systematically stronger associations found between WTL and seven other well-established SWB constructs when WTL was measured by the 5-item scale rather than by the single-item measure, and by the results of a hierarchical regression analysis performed to predict positive morale at T3, which showed that the predictive power of the T1-5 items of the WTL-Scale was significantly greater than that of the single-item. The results of these comparative analyses, which indicate that in comparison to the single-item measure, the 5-item scale is more sensitive to a wider range of SWB aspects depicted by other SWB measures, lend support to the classic measurement theory (Bowling, 2005). In conclusion, based on these results, the CFA models which show that each of the 5 items contributes significantly to measurement at each point of data collection, the goodness of fit indices that strongly support the measurement properties of scale, and the good psychometric properties of the WTL-Scale, we recommend to measure the WTL construct by the 5-item WTL-scale rather than by the singleitem measure. Similar correlations of the WTL with other indicators of SWB were found in previous studies as well (e.g., Carmel, 2001a, 2011). However, these repeated significant correlations were not very high, indicating that the WTL is a different and unique concept, and as such, the WTL-Scale has an additive value in that it evaluates additional aspects to those assessed by other measures of SWB. One of these additional facets is the motivation to cling to life, an aspect embedded in people's WTL, but lacking in other well-known indicators of SWB (Carmel, 2001a, 2011). Evaluation of the commitment to life aspect is of special importance in old age when 17
people become increasingly exposed to decline in their quality-of-life due to age-related losses in almost all areas of their lives (health, function, economic resources, social relations etc.), experiences which intensify the elderly person's awareness to the approaching end of their lives. The generalizability of our results is limited because this study is based on data from a single sample of community-dwelling older Israelis. Also, the 29% of participants who dropped out from the second and third stages of this study were a significantly weaker group that ranked lower than the remaining participants on our measures of health and all indicators of SWB except for loneliness and WTL, both of which are probably more stable constructs affected by more extreme or specific life events. Although the latent structure of the WTL-Scale was found to be stable over time, and as regards internal reliability and validity of the WTL-Scale our results are similar to those reported in previous Israeli studies using this scale (Carmel, 2011), further support to our findings is needed by use of the WTL-Scale in longitudinal studies of various groups of elderly people (in terms of health status and socio-cultural background) living within the same or in different societies. Considering the theoretical structure of the WTL as an expression of two different facets – the instinctual which is a natural phenomenon common to all humans, and the cognitiveemotional, which is influenced by socio-cultural factors including cultural beliefs and life circumstances (Carmel, 2001a; 2011), use of the WTL-Scale in various socio-cultural groups is expected to result in both, similarities and differences: For example, we expect to find similarities in the latent structure of the scale when evaluated in different social groups. Based on previous findings which showed the important role of WTL in long-term survival in Israel and Finland (Carmel et al., 2007; Karppinen et al., 2012), or the effects of WTL on life-satisfaction in proximity to death (Carmel et al., 2013), we would also expect to find similar effects of the 18
strength of the WTL on other end-of-life related phenomena across socio-cultural groups. However, similar to results of previous studies (Beadle et al., 2004; Chochinov et al., 2005; Ellison, 1969; Huohvanainen et al., 2012), including studies on preferences for the prolongation of life in severe illness conditions (e.g., Carmel & Mutran, 1997a), we expect to find differences within and across societies among people with different beliefs, and/or people living under different health-related life circumstances and psycho-social conditions. In summary, we suggest that although the strength of the WTL may vary among individuals as well as in different cultures and social groups, the effects of the WTL on significant end of life related phenomena and the latent structure of the WTL-Scale will remain similar. These hypotheses, and the reliability and validity of the WTL-Scale, should be further supported in replications of our analyses in other societies and socio-cultural groups within the same societies, as well as among patients suffering from severe diseases and/or functional limitations. Conclusion The results of this study indicate that the WTL-Scale is a concise, reliable and valid tool for evaluating the WTL of older adults. Considering that WTL is a unique and important indicator of SWB in old age, we recommend using the WTL concept and the 5-item WTL-Scale in research, as well as in practice involving interventions for maintaining and enhancing elderly persons' SWB, and in planning care towards the end of life.
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Appendix 1: The Will-to-Live Scale (WTLS). Please circle the number under the most appropriate response for you: 1. In your current condition, would you want to continue living for many years? I don’t know I think that not Certainly not
Certainly, yes I think I would 5
4
3
2
I have no will to live
1
0
2. In comparison to people your age, how would you evaluate your will to live? Much stronger
5
stronger
not stronger and not weaker
4
3
weaker
much weaker
2
1
I have no will to live
0
3. How would you evaluate your will-to-live today, in comparison to what it was when you were younger? Much stronger 5
stronger 4
as it was when I was younger 3
weaker
much weaker
2
1
I have no will to live 0
4. If you would evaluate your will to live on a scale from 0 to 5, would you say that it is: The strongest possible 5
strong 4
intermediate 3
weak
very weak
2
1
I have no will to live 0
5. In the last year, would you say that your will-to-live: Became much became stronger stronger 5
4
has not changed 3
weakened
2
much weakened 1
I had no will to live
0
---------------------------------------------------------------------------------------------------------------------------Notes: - The overall score is based on the average score of the responses to all five questions. - Question number 4 can be used as a single item measure to evaluate the WTL (alternatively).
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Table 1. Summary specifications (invariance analyses) across three points of measurement.
χ2
df
Δ χ2
Δdf
SRMR
CFI
baseline
43.500
12
--
--
.009
.99
.032 (.022 - .042)
Item 1
43.500
14
0
2
.009
.99
.028 (.019 - .038)
Item 2
43.500
16
0
2
.009
.99
.026 (.017 - .035)
Item 3
43.500
18
0
2
.009
.99
.023 (.015 - .032)
Item 4
43.500
20
0
2
.009
.99
.021 (.013 - .030)
Item 5
43.500
20
0
2
.009
.99
.021 (.013 - .030)
Model
RMSEA (CL90)
Note. df = degrees of freedom, SRMR = Standardized Root Mean Square Residual, CFI = Comparative Fit Index; RMSEA = Root Mean Square Error of Approximation. CL90 = 90% Confidence Limits.
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Figure1. Confirmatory latent factor model will-to-live, three points of data collection.
T1: .69 (15.17)
Item 1
T2: .69 (17.94) T3: .71 (21.04)
Item 2
T1: .69 (15.37) T2: .83 (21.07) T3: .86 (26.43)
T1: .39 (7.21) T2: .43 (9.06) T3: .50 (10.9)
Item 3
T1: .75 (16.15) T2: .77 (20.01)
Will To Live
T3: .85 (26.16)
Item 4
T1: .71 (15.52) T2: .73 (18.94) T3: .75 (22.55)
T1: .63 (15.19)
Item 5
T2: .70 (17.94) T3: .77 (21.04)
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Note. Parameters expressed as standardized estimates. Parenthetical numbers indicate significance levels for coefficients (statistically significant t values > 6.31, p < .01).
28
