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Quality of life and sense of coherence in young people and adults with uncomplicated epilepsy: A longitudinal study
Epilepsy & Behavior 47 (2015) 127–131
Contents lists available at ScienceDirect
Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh
Quality of life and sense of coherence in young people and adults with uncomplicated epilepsy: A longitudinal study Mona Persenius a,⁎, Ingrid Rystedt a, Bodil Wilde-Larsson a,b, Carina Bååth a a b
Faculty of Health, Science, and Technology, Department of Health Sciences, Karlstad University, Karlstad, Sweden Department of Nursing and Mental Health, Faculty of Public Health, Hedmark University College, Elverum, Norway
a r t i c l e
i n f o
Article history: Received 6 February 2015 Revised 30 March 2015 Accepted 2 April 2015 Available online 9 May 2015 Keywords: Adolescents Epilepsy Longitudinally Quality of life Sense of coherence Adults
a b s t r a c t Objectives: The aim of the study was, in a ten-year follow-up, to describe and explore potential changes in quality of life and sense of coherence in relation to gender differences among persons with epilepsy in the transition from adolescence to adulthood. Materials and methods: A longitudinal study of sense of coherence (SOC) and quality of life with repeated measurement design (1999, 2004, and 2009) was conducted in a population of persons (n = 69) who were aged 13–22 years in 1999 and 23–33 years in 2009. The Quality-of-Life Index (QLI) and the Sense of Coherence (SOC) scale were used. Results: There was a significant decrease (p ≤ 0.001) in seizures compared with the 2004 results, mainly among the women (p = 0.003). When comparing the total QLI scores, no significant differences were found between the three data collections and there were no differences in total scores between men and women. There was a decrease in the SOC total score over the 10-year period study. Total SOC was significantly higher among those being 30–33 years old compared to those being 23–29 years old (p = 0.014) and among those having a driving license (p = 0.029) compared to those not having a driving license. Conclusions: Both quality of life and sense of coherence are important for maintaining health and well-being. Promoting health and well-being requires effective high-quality multidisciplinary person-centered care. © 2015 Elsevier Inc. All rights reserved.
1. Introduction According to the World Health Organization (WHO), epilepsy is one of the world's most common serious brain disorders, affecting about 50 million people globally [1]. In Sweden, the prevalence of active epilepsy is approximately 0.6–0.7%, which means that about 60,000 people have epilepsy, of which 50,000 are adults and 10,000 are children [2]. However, reported incidence rates may vary because of differences in age structures among different countries [3] and because of an array of utilized age definitions. For example, the WHO [4] has defined adolescents as young people between the ages of 10 and 19 years, while the United Nations (UN) has defined youth to be people between 15 and 24 years [5]. Even if the goal of epilepsy treatment is to control seizures with minimum side effects [6], only about 70% of people with epilepsy achieve this goal with antiepileptic drugs (AEDs) [1]. Persons diagnosed with epilepsy are more likely to experience lower quality of life (QOL) than the general population because of seizures and medical–psychiatric and psychosocial problems [7] as well as perceived stigma and discrimination [1,7]. Women with epilepsy tend to have ⁎ Corresponding author. Tel.: +46 547002291. E-mail address: [email protected] (M. Persenius).
http://dx.doi.org/10.1016/j.yebeh.2015.04.002 1525-5050/© 2015 Elsevier Inc. All rights reserved.
lower QOL than men with epilepsy [8–10]. Age and duration of the epilepsy diagnosis can have a significant negative association with healthrelated QOL in epilepsy [11]. Seizure severity [12], treatment side effects [13], and depression [12] are all found to be clinically significant predictors of QOL. However, there are [13] no data to suggest that age, gender, education, family status, comorbidity, seizure type, age at seizure onset, and epilepsy duration significantly affect the overall QOL as measured with the Quality of Life in Epilepsy Inventory (QOLIE-31) [13]. Sense of coherence (SOC) reflects a person's ability to cope with difficult or stressful situations. SOC among young people and adults with epilepsy has been sparsely researched. The findings from the first data collection in this project indicate that females (13–22 years) have a lower SOC compared with males (13–22 years) (p = 0.003) [14]. A study following young people and adults over a 10-year period is of particular interest because it includes the transition from adolescent to adulthood. Though some gender differences regarding QOL and SOC have been noted in previous research, there is a need for a longer follow-up of this cohort. The aim of the study was, therefore, in a ten-year follow-up, to describe and explore potential changes in quality of life and sense of coherence in relation to gender differences among persons with epilepsy in the transition from adolescence to adulthood.
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2. Materials and methods 2.1. Design
Baseline 1999 Assessed for eligibility (n=193)
A prospective and longitudinal study of sense of coherence and quality of life with repeated measurement design was carried out. 2.2. Sample and data collection At baseline, in 1999, all adolescents and young adults (n = 193) aged 13 to 22 years, who had been diagnosed with uncomplicated epilepsy (i.e., epilepsy with no initially associated neurological impairment) and registered as having an epilepsy diagnosis (defined as at least two unprovoked epileptic seizures), in four Swedish hospitals [15] were invited to participate. The inclusion criteria were having experienced at least one epileptic seizure during the last year and/or being on epileptic drug treatment for epilepsy. Individuals with additional neurological impairments, benign childhood epilepsy, or other diseases or handicaps that were considered to substantially impact on QOL were excluded, leaving 151 participants (78%) in the study: 84 females and 67 males [15]. In 2004, the first follow-up study with these persons, then 18–27 years old, was carried out, and a total of 102 out of 146 (69.9%) traceable persons of the 151 participants from 1999 returned the completed Quality-of-Life Index (QLI) questionnaires [16]. Medical information was extracted from the patients' records by two physicians. Ninety-seven persons out of the 146 (66.4%) returned completed questionnaires regarding their sense of coherence [17]. The two most common diagnoses in 2004, in accordance with the ICD-10, were “generalized idiopathic epilepsy and epileptic syndrome” (52.2%) and “partial symptomatic epilepsy and epileptic syndrome with complex partial seizures” (20.3%). Other diagnoses were epilepsy, nonspecified (14.5%); partial symptomatic epilepsy and epileptic syndrome with simple seizures (5.8%); grand mal seizures, nonspecified (4.3%); other generalized epilepsy and epileptic syndromes (1.4%); and other epilepsy (1.4%). In 2009, a second follow-up data collection on sense of coherence and quality of life was carried out. The individuals from previous data collections were identified by a research assistant, and they were invited to participate in this follow-up study. In addition to the questions included in the previous follow-up, questions regarding personality and quality of care were included; these were consequently not part of the longitudinal study and will be reported elsewhere. The questionnaire with a prestamped envelope was mailed to the individuals. Written information about the study was included. After about one month, a reminder was sent to those who had not responded. Those who still did not respond were contacted by phone by the research assistant. If they agreed to participate, another copy of the questionnaire was sent to them. In total, eighty-seven out of 128 traceable persons (53.9%) responded. Sixty-nine persons had now responded to both the QLI and SOC scale at all three data collection periods (Fig. 1). 2.3. Questionnaires The self-administered generic version of the Quality-of-Life Index (QLI) developed in 1984 by Ferrans and Powers [18] was used. The QLI comprises a total of 68 items phrased as questions. The first section is related to satisfaction with specific areas of life (34 questions), while the second section is related to the importance, to the individual, of these same areas of life (34 questions). The 6-point response scale ranges from 1 = very dissatisfied/very unimportant to 6 = very satisfied/very important. Total scores range from 0 to 30, with higher scores indicating better QOL. In this study, Cronbach's alpha values [19] for the QLI were 0.89 (baseline in 1999), 0.97 (first follow-up in 2004), and 0.96 (second follow-up in 2009).
Non-response (35) Benign childhood epilepsy (n=7)
Baseline questionnaire returned (n=151)
5 year follow-up 2004 Non-traceable in the 5-year follow-up 1999 (n=5) Traceable in the 5-year follow-up (n=146)
Completed QLI questionnaire returned (n=102) Completed SOC questionnaire returned (n=97)
10 year follow-up 2009 Non-traceable in the 146 included in 2004 (n=18) Traceable in the 10-year follow-up (n=128) Questionnaire returned (n=87) Completed QLI and SOC questionnaires at all three data collection periods (n=69)
Fig. 1. Flow chart.
The Sense of Coherence (SOC) scale developed by Antonovsky comprises comprehensibility, manageability, and meaningfulness [20]. In this study, the 13-item version [21] was used at all three occasions. The 7-point response scale ranges from 1 to 7, with higher scores representing higher sense of coherence. The total SOC score was calculated by adding each item's score, ranging from 13 to 91, with higher scores representing stronger SOC. In the present study, Cronbach's alpha values were 0.51 (baseline in 1999), 0.89 (first follow-up in 2004), and 0.87 (second follow-up in 2009). In addition, some background and study-specific questions were included in the questionnaire (see Table 1).
2.4. Analysis Statistical analyses were performed using SPSS, version 20.0. Descriptive statistics with frequencies, percent, range, mean, and standard deviation were used to describe the study sample. Estimates of internal consistency were established with Cronbach's alpha [19]. The mean SOC score and mean QLI score from the first (1999), second (2004), and third (2009) data collection points were compared using Friedman's two-way analysis of variance by ranks test and the Wilcoxon signedrank test, while differences between two independent groups were analyzed using the Mann–Whitney U-test [22]. For nonparametric-related samples, McNemar's test was used. The correlation between QLI and SOC was tested with Spearman's rho. The epilepsy diagnoses were categorized based on the ICD-10 codes used in 2004: “focal seizures” (ICD-10 code 40.1 or 40.2); “generalized
M. Persenius et al. / Epilepsy & Behavior 47 (2015) 127–131
129
Table 1 Frequency of seizures in 2004 and 2009 by gender. Frequency of seizures
2004
NOnce a week NOnce a month bOnce a month Never/less than once a year Missing
2009
Total (n = 69)
Men (n = 21)
Women (n = 48)
Total (n = 69)
Men (n = 21)
Women (n = 48)
– 3 20 46 –
– – 7 14 –
– 3 13 32 –
1 3 4 45 16
– 1 1 14 5
1 2 3 31 11
seizures” (ICD-10 code 40.3, 40.4, or 40.6); and finally, “seizures not classified” (ICD-10 code 40.8 or 40.9). The classification used to determine how well the epilepsy was controlled was the one designed by Ericsson and Koivikko [23]: good control = no seizures during the last year, partial control = one or more seizures during the last year but not more than one per month, and poor control = more than one seizure per month. Changes in QOL and SOC were calculated as the values at data collection 2 (2004) minus the values at baseline (1999) and the values at data collection 3 (2009) minus the values at data collection 2 (2004). All tests were two-tailed and were assessed at a significance level of p b 0.05. 2.5. Ethical considerations The study was approved by a regional research committee in Sweden (reference numbers 98-312 (1999), 03-532 (2004), and C 2009/253 (2009)). The study was conducted in accordance with the ethical principles of human research [24]. 3. Results The results showed that sixty-nine out of the 158 persons who accepted the invitation at baseline (43.7%) had completed the questionnaires at all three occasions (1999, 2004, and 2009). At the end of the study (2009), 69 of these people were aged between 23 and 33 years (mean: 28.9, SD: 2.78). Forty-eight were females (69.6%) and 21 males (30.4%). At the final follow-up, more than half of the respondents (60.8%) were living in a relationship, that is, married/cohabitating with child(ren) (37.3%), married/cohabitating without child(ren) (20.9%), or living alone (4.5%). Almost one-third (32.8%) were unmarried/cohabiting without child(ren), and 3% were unmarried/cohabitating with child(ren). One person had not yet moved out of the parental home (1.5%). The majority were employed (68.7%), ten were students (14.9%), seven were unemployed (10.4%), and two were on sick leave (3%). Two had other, nonspecified, work conditions (3.0%). Among those
who had employment, it was on either a full-time (49.3%) or parttime (19.4%) basis. A few had other – nonspecified – self-reported dysfunctions (10.4%). Two-thirds had a driving license (66.7%). A total of eight persons still had seizures in 2009 (11.6%) (two men and six women) (see Table 1). This was a significant decrease (p ≤ 0.001) compared to the 2004 results, mainly among the women (p = 0.003). 3.1. QLI and SOC (1999–2009) When comparing the total QLI scores, no significant differences were found between the three data collections (see Table 2) and there were no differences in total scores between men and women. There were no significant associations between QLI and age, civil status, work condition, having a driving license, frequencies of seizures, or type of seizures. Between 2004 and 2009, the total score of sense of coherence (SOC scale) decreased significantly (p = 0.003), which was also the case between 1999 and 2009 (p ≤ 0.001) (Table 2). This decrease included both female (p = 0.040) and male (p = 0.024) respondents between 2004 and 2009. The SOC was significantly higher among those being 30–33 years old compared to those being 23–29 years old (p = 0.014) and among persons with a driving license (p = 0.029) compared to those not having a driving license. There were no significant associations between SOC and civil status, work condition, frequencies of seizures, or type of seizures. There were significant positive correlations (p b 0.001) between SOC and QLI at baseline and at data collection points 2 and 3. The more positive the QLI, the more SOC increased. 4. Discussion To our knowledge, this is the first study to use a 10-year longitudinal design to describe and explore potential changes in quality of life and
Table 2 Quality-of-Life Index (QLI) scores, total and subscales, and total sense of coherence (SOC) for young people with epilepsy in 1999, 2004, and 2009. 1999
QLI Totalc Health and functioning Socioeconomics Psychological/spiritual Family and friends Total SOCd a b c d
2004
p-Valuea
2009
n
Mean
SD
Range
n
Mean
SD
Range
n
Mean
SD
Range
69 69 69 68 69 69
22.16 22.49 22.00 20.85 23.46 64.99
3.74 3.65 4.42 4.94 4.58 13.11
11.7–29.4 12.1–29.0 10.3–30.0 3.5–30.0 11.6–30.0 34–88
69 69 69 68 69 69
22.16 22.13 22.25 20.92 24.86 61.84
3.76 4.05 4.16 5.01 4.42 13.13
11.7–29.4 11.3–29.2 12.8–30.0 3.3–30.0 13.0–30.0 30–87
69 69 68 68 68 69
22.36 22.53 21.83 21.48 24.11 58.82
4.43 4.34 5.04 5.49 6.17 11.64
8.6–29.4 10.2–29.2 7.3–30.0 5.5–30.0 0.0–30.0 31–78
Friedman's two-way analysis of variance by ranks, p-value ≤ 0.05. Wilcoxon signed-rank test (exact sig. 2-tailed), p-value ≤ 0.05. Total scores range from 0 to 30, with high scores indicating better QOL. Total SOC is ranging from 13 to 91, with higher scores indicating stronger SOC.
.784 .173 .755 .585 .020 0.002
5-year follow-up (2004–2009)
10-year follow-up (1999–2009)
p-Valueb
p-Valueb
.846 .435 .359 .262 .644 0.003
.832 .760 .627 .214 .230 b0.001
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sense of coherence in relation to gender in adolescents and adults with uncomplicated epilepsy. The result showed a significant decrease (p ≤ 0.001) in seizures compared with the 2004 results, mainly among the women (p = 0.003). Even though the study focused on uncomplicated epilepsy, it is somewhat surprising to find that the vast majority of the persons were seizure-free after ten years. About 70% of patients with epilepsy experience control of seizures with AEDs according to the WHO [1]. However, in 2009, there were missing responses regarding the participant's seizures, which suggest that the results should be interpreted with caution. The results showed no difference in total QLI scores across the study time periods. When comparing our results with those in a Swedish population of 18- to 30-year-olds where the overall mean score was found to be 21.3 [25], the total QLI score during the entire time period in our study was higher. This finding correlates with those of other studies. Among adolescents with congenital heart disease, the QOL was significantly higher compared with the control group [26]. It has been suggested that QOL and health are two separate constructs, although they are not mutually exclusive [7], something that could explain why persons with epilepsy are reporting high quality of life in spite of being affected by epilepsy. Another explanation could be that persons with disorders that were considered to affect QOL in a substantial way were excluded. In our study, the total score of SOC significantly decreased between 1999 and 2009, which is the period when the persons grew up with epilepsy, from age 13–22 years to age 23–33 years. The research literature is inconsistent regarding whether SOC is stable or changes over time. According to a salutogenic perspective [20], SOC should be relatively stabilized at the end of early adulthood [20], although in a 5-year follow-up study in a general Swedish population, in those aged 25–74 years, SOC was stable only when scores were high from the outset [27]. In our study, SOC was significantly higher among those aged 30–33 years compared to those aged 23–29 years (p = 0.014), indicating a stabilization of SOC that is in line with other studies [20]. Reviewing previous research [28], there have been few studies supporting the notion of a stable SOC throughout the lifespan; in contrast, they observed that it tends to increase with age. When comparing our results with a study in the general population aged 15 to 29 years (62.74) [29], the total SOC score was somewhat higher at baseline in 1999 (64.99). It is known that individuals with stronger SOC tend to cope with their ill health better compared to those with a weaker SOC [20,27]. One-third of the persons did not have a driving license; however, no impact on their QOL was shown despite that it is often cited as a lifestyle limitation [7]. This contradicts other findings where driving significantly affected QOL [12]. Total SOC, however, was significantly lower among persons without a driving license (p = 0.029) compared to persons with a driving license in our study, indicating a level of discontent with the situation. The results showed that SOC is strongly associated with the QLI, a finding well in line with the results from other studies [30]. In addition, SOC has been identified as a determinant of QOL, over time, in female survivors of acute myocardial infarction [31] and an important resource for quality of life among patients with congenital heart disease [26]. The SOC concept is considered to be a health resource influencing QOL [30,31], and it has been suggested that a salutogenic approach in clinical practice, focusing on patient resources and strengths rather than on problems and limitations, could optimize the QOL for people affected by epilepsy [31]. 4.1. Methodological concerns We had a 43% response rate in the 10-year follow-up, indicating that many of the study participants deemed the study to be highly important. With only a few exceptions, the response rates to individual QLI
items were consistent, with a limited number of internally missing data. Regarding SOC, there was one internally missing data point (n = 1) for each data collection time period. The use of well-known and validated instruments may be considered as strength of our study. In this study, Cronbach's alpha values for the QLI were 0.89 (baseline in 1999), 0.97 (first follow-up in 2004), and 0.96 (second follow-up in 2009). The Cronbach's alpha values regarding SOC ranged between 0.70 and 0.92 in 127 studies according to Eriksson and Lindström [30]. Here, in the present study, Cronbach's alpha values were 0.51 (baseline in 1999), 0.89 (first follow-up in 2004), and 0.87 (second follow-up in 2009). 5. Conclusion To our knowledge, our study is the first to report a stable QLI over a ten-year period among persons with uncomplicated epilepsy, during the transition from adolescence to adulthood, while there was a decrease in SOC during the same time period. Both quality of life and sense of coherence are important resources for maintaining health and well-being. Promoting health and wellbeing requires effective high-quality multidisciplinary person-centered care. Health-care professionals have an important role in supporting individuals in their daily lives. Aside from being knowledgeable about QOL and SOC in persons with epilepsy, they should be empowering patients and their relatives through education and psychosocial support and involving them in decision-making regarding their treatment and care. Further areas for research include evaluation of the effect of interventions aimed at enhancing or maintaining health and well-being in persons with epilepsy. Acknowledgment We gratefully thank senior lecturer Lena Räty for the design and planning of this study, lecturer (and research assistant) Maria Bystedt for the data collection, and Professor Jari Appelgren for his statistical advice. Sincere gratitude is also expressed to the persons with epilepsy, the study participants, who made this study possible. Conflict of interest The authors declare they have no competing interest and no financial disclosures. References [1] WHO. Epilepsy. Available at: http://www.who.int/mediacentre/factsheets/fs999/en/ . ; 2012. [retrieved 2014-10-08]. [2] Ben-Menachem E, Olsson I, Uvebrant P. Epilepsy. In: Örtqvist P, editor. Läkemedelsboken Läkemedelsverket; 2014. p. 972–81 [http://www.lakemedelsboken.se/ (retrieved 201404-25)]. [3] Forsgren L, Beghib A, Õun A, Sillanpää M. The epidemiology of epilepsy in Europe — a systematic review. Eur J Neurol 2005;12:245–53 [http://onlinelibrary.wiley.com/ doi/10.1111/j.1468-1331.2004.00992.x/pdf]. [4] World Health organization. Adolescent friendly health services: an agenda for change. Geneva: WHO; 2002[http://www.who.int/maternal_child_adolescent/ documents/fch_cah_02_14/en/ (retrieved 2014-04-25)]. [5] United Nations. http://www.un.org/esa/socdev/documents/youth/fact-sheets/ youth-definition.pdf. [6] Talati R, Scholle JM, Phungh OJ, Baker WL, Baker EL, Ashaye A, et al. Effectiveness and safety of antiepileptic medications in patients with epilepsy. (Internet) Comparative effectiveness reviews, no. 40. Rockville (MD): Agency for Healthcare Research and Quality (US); 2011[http://www.ncbi.nlm.nih.gov/ books/NBK83937/ (retrieved 2014-11-10)]. [7] Jacoby A, Snape D, Baker G. Determinants of quality of life in people with epilepsy. Neurol Clin 2009;27(4):843–63. [8] Benavente-Aguilar I, Morales-Blánquez C, Rubio EA, Rey JM. Quality of life of adolescents suffering from epilepsy living in the community. J Paediatr Child Health 2004; 40:110–3. [9] Räty L, Hamrin E, Söderfeldt B. Quality of life in newly-debuted epilepsy, an empirical study. Acta Neurol Scand 1999;100:221–6.
M. Persenius et al. / Epilepsy & Behavior 47 (2015) 127–131 [10] Witt J-A, Werhahn J, Krämer G, Ruckes C, Trinka E, Helmstaedter C. Cognitive– behavioral screening in elderly patients with new-onset epilepsy before treatment. Acta Neurol Scand 2014;130:172–7. [11] Edefonti V, Bravi F, Turner K, Beghi E, Canevini MP, Ferraroni M, et al. Health-related quality of life in adults with epilepsy: the effect of age, age at onset and duration of epilepsy in a multicenter Italian study. BMC Neurol 2011;11(33) [http://www. biomedcentral.com/1471-2377/11/33 (retrieved 2014-11-14)]. [12] Jehi L, Tesar G, Obuchowski N, Novak E, Najm I. Quality of life in 1931 adult patients with epilepsy: seizures do not tell the whole story. Epilepsy Behav 2011;22:723–7. [13] Auriel E, Landov H, Blatt I, Theitler J, Gandelman-Marton R, Chistik V, et al. Quality of life in seizure-free patients with epilepsy on monotherapy. Epilepsy Behav 2009;14: 130–3. [14] Räty L, Larsson G, Söderfeldt A, Wilde Larsson B. Psychosocial aspects of health in adolescence: the influence of gender, and general self-concepts. J Adolesc Health 2005; 36:530.e21–8. [15] Räty L, Wilde-Larsson B, Söderfeldt B. Health-related quality of life in youth: a comparison between adolescents and young adults with uncomplicated epilepsy and healthy controls. J Adolesc Health 2003;33:252–8. [16] Räty L, Wilde-Larsson B. Quality of life in young adults with uncomplicated epilepsy. Epilepsy Behav 2007:142–7. [17] Gauffin H, Landtblom A-M, Räty L. Self-esteem and sense of coherence in young people with uncomplicated epilepsy: a 5-year follow-up. Epilepsy Behav 2010;17: 520–4. [18] Ferrans CE, Powers MJ. Psychometric assessment of the quality of life index. Res Nurs Health 1992;15:29–38. [19] Cronbach L. Coefficient alpha and the internal structure of tests. Psychometrika 1951;16:297–334. [20] Antonovsky A. The structure and properties of the sense of coherence scale. Soc Sci Med 1993;36(6):725–33. [21] Guldvog B. Spørsmål om livet. Aron Antonovsky's sence of coherence scale. Sentralsykehuset I Akershus: Stiftelsen for Helsetjenste forskning; 1996 (in Norwegian).
131
[22] Polit DF, Beck CT, editors. Nursing research: generating and assessing evidence for nursing practice. 9th ed. Philadelphia: Lippincott Williams and Wilkins; 2012. [23] Ericsson KJ, Koivikko MJ. Prevalence, classification and severity of epilepsy and epileptic syndromes in children. Epilepsia 1997;38(12):1275–82. [24] Northern Nurses Federation. Ethical guidelines for nursing research in the Nordic countries. Vard Nord Utveckl Forsk Nord J Nurs Res 2003;23(4):1–19. [25] Gullberg MT, Hollman-Frisman G, Ek A-K. Reference values for the Quality of Life Index in the general Swedish population 18–80 years of age. Qual Life Res 2010; 19:751–60. [26] Apers S, Luykx K, Rassart J, Goossens E, Budts W, Moons P. Sense of coherence is a predictor of perceived health in adolescents with congenital heart disease: a crosslagged prospective study. Int J Nurs Stud 2013;50:776–85. [27] Nilsson B, Holmgren L, Stegmayr B, Westman G. Sense of coherence — stability over time and relation to health, disease, and psychosocial changes in a general population: a longitudinal study. Scand J Public Health 2003;31:297–304. [28] Eriksson M, Lindström B. Validity of Antonovsky's sense of coherence scale: a systematic review. J Epidemiol Community Health 2005;59:460–6. http://dx.doi. org/10.1136/jech.2003.018085. [29] Larsson G, Kallenberg K-O. Sense of coherence, socioeconomic conditions and health. Interrelationships in a nation-wide Swedish sample. J Public Health 1996; 6:175–80. [30] Eriksson M, Lindström B. Antonovsky's sense of coherence scale and its relation with quality of life: a systematic review. J Epidemiol Community Health 2007;61:938–44. http://dx.doi.org/10.1136/jech.2006.056028. [31] Norekvål TM, Fridlund B, Moons P, Nordrehaug JE, Saevareid HI, Wentzel-Larsen T, et al. Sense of coherence a determinant of quality of life over time in older female acute myocardial infarction survivors. J Clin Nurs 2009;19:820–31. http://dx.doi. org/10.1111/j.1365-2702.2009.02858.x.
Contents lists available at ScienceDirect
Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh
Quality of life and sense of coherence in young people and adults with uncomplicated epilepsy: A longitudinal study Mona Persenius a,⁎, Ingrid Rystedt a, Bodil Wilde-Larsson a,b, Carina Bååth a a b
Faculty of Health, Science, and Technology, Department of Health Sciences, Karlstad University, Karlstad, Sweden Department of Nursing and Mental Health, Faculty of Public Health, Hedmark University College, Elverum, Norway
a r t i c l e
i n f o
Article history: Received 6 February 2015 Revised 30 March 2015 Accepted 2 April 2015 Available online 9 May 2015 Keywords: Adolescents Epilepsy Longitudinally Quality of life Sense of coherence Adults
a b s t r a c t Objectives: The aim of the study was, in a ten-year follow-up, to describe and explore potential changes in quality of life and sense of coherence in relation to gender differences among persons with epilepsy in the transition from adolescence to adulthood. Materials and methods: A longitudinal study of sense of coherence (SOC) and quality of life with repeated measurement design (1999, 2004, and 2009) was conducted in a population of persons (n = 69) who were aged 13–22 years in 1999 and 23–33 years in 2009. The Quality-of-Life Index (QLI) and the Sense of Coherence (SOC) scale were used. Results: There was a significant decrease (p ≤ 0.001) in seizures compared with the 2004 results, mainly among the women (p = 0.003). When comparing the total QLI scores, no significant differences were found between the three data collections and there were no differences in total scores between men and women. There was a decrease in the SOC total score over the 10-year period study. Total SOC was significantly higher among those being 30–33 years old compared to those being 23–29 years old (p = 0.014) and among those having a driving license (p = 0.029) compared to those not having a driving license. Conclusions: Both quality of life and sense of coherence are important for maintaining health and well-being. Promoting health and well-being requires effective high-quality multidisciplinary person-centered care. © 2015 Elsevier Inc. All rights reserved.
1. Introduction According to the World Health Organization (WHO), epilepsy is one of the world's most common serious brain disorders, affecting about 50 million people globally [1]. In Sweden, the prevalence of active epilepsy is approximately 0.6–0.7%, which means that about 60,000 people have epilepsy, of which 50,000 are adults and 10,000 are children [2]. However, reported incidence rates may vary because of differences in age structures among different countries [3] and because of an array of utilized age definitions. For example, the WHO [4] has defined adolescents as young people between the ages of 10 and 19 years, while the United Nations (UN) has defined youth to be people between 15 and 24 years [5]. Even if the goal of epilepsy treatment is to control seizures with minimum side effects [6], only about 70% of people with epilepsy achieve this goal with antiepileptic drugs (AEDs) [1]. Persons diagnosed with epilepsy are more likely to experience lower quality of life (QOL) than the general population because of seizures and medical–psychiatric and psychosocial problems [7] as well as perceived stigma and discrimination [1,7]. Women with epilepsy tend to have ⁎ Corresponding author. Tel.: +46 547002291. E-mail address: [email protected] (M. Persenius).
http://dx.doi.org/10.1016/j.yebeh.2015.04.002 1525-5050/© 2015 Elsevier Inc. All rights reserved.
lower QOL than men with epilepsy [8–10]. Age and duration of the epilepsy diagnosis can have a significant negative association with healthrelated QOL in epilepsy [11]. Seizure severity [12], treatment side effects [13], and depression [12] are all found to be clinically significant predictors of QOL. However, there are [13] no data to suggest that age, gender, education, family status, comorbidity, seizure type, age at seizure onset, and epilepsy duration significantly affect the overall QOL as measured with the Quality of Life in Epilepsy Inventory (QOLIE-31) [13]. Sense of coherence (SOC) reflects a person's ability to cope with difficult or stressful situations. SOC among young people and adults with epilepsy has been sparsely researched. The findings from the first data collection in this project indicate that females (13–22 years) have a lower SOC compared with males (13–22 years) (p = 0.003) [14]. A study following young people and adults over a 10-year period is of particular interest because it includes the transition from adolescent to adulthood. Though some gender differences regarding QOL and SOC have been noted in previous research, there is a need for a longer follow-up of this cohort. The aim of the study was, therefore, in a ten-year follow-up, to describe and explore potential changes in quality of life and sense of coherence in relation to gender differences among persons with epilepsy in the transition from adolescence to adulthood.
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2. Materials and methods 2.1. Design
Baseline 1999 Assessed for eligibility (n=193)
A prospective and longitudinal study of sense of coherence and quality of life with repeated measurement design was carried out. 2.2. Sample and data collection At baseline, in 1999, all adolescents and young adults (n = 193) aged 13 to 22 years, who had been diagnosed with uncomplicated epilepsy (i.e., epilepsy with no initially associated neurological impairment) and registered as having an epilepsy diagnosis (defined as at least two unprovoked epileptic seizures), in four Swedish hospitals [15] were invited to participate. The inclusion criteria were having experienced at least one epileptic seizure during the last year and/or being on epileptic drug treatment for epilepsy. Individuals with additional neurological impairments, benign childhood epilepsy, or other diseases or handicaps that were considered to substantially impact on QOL were excluded, leaving 151 participants (78%) in the study: 84 females and 67 males [15]. In 2004, the first follow-up study with these persons, then 18–27 years old, was carried out, and a total of 102 out of 146 (69.9%) traceable persons of the 151 participants from 1999 returned the completed Quality-of-Life Index (QLI) questionnaires [16]. Medical information was extracted from the patients' records by two physicians. Ninety-seven persons out of the 146 (66.4%) returned completed questionnaires regarding their sense of coherence [17]. The two most common diagnoses in 2004, in accordance with the ICD-10, were “generalized idiopathic epilepsy and epileptic syndrome” (52.2%) and “partial symptomatic epilepsy and epileptic syndrome with complex partial seizures” (20.3%). Other diagnoses were epilepsy, nonspecified (14.5%); partial symptomatic epilepsy and epileptic syndrome with simple seizures (5.8%); grand mal seizures, nonspecified (4.3%); other generalized epilepsy and epileptic syndromes (1.4%); and other epilepsy (1.4%). In 2009, a second follow-up data collection on sense of coherence and quality of life was carried out. The individuals from previous data collections were identified by a research assistant, and they were invited to participate in this follow-up study. In addition to the questions included in the previous follow-up, questions regarding personality and quality of care were included; these were consequently not part of the longitudinal study and will be reported elsewhere. The questionnaire with a prestamped envelope was mailed to the individuals. Written information about the study was included. After about one month, a reminder was sent to those who had not responded. Those who still did not respond were contacted by phone by the research assistant. If they agreed to participate, another copy of the questionnaire was sent to them. In total, eighty-seven out of 128 traceable persons (53.9%) responded. Sixty-nine persons had now responded to both the QLI and SOC scale at all three data collection periods (Fig. 1). 2.3. Questionnaires The self-administered generic version of the Quality-of-Life Index (QLI) developed in 1984 by Ferrans and Powers [18] was used. The QLI comprises a total of 68 items phrased as questions. The first section is related to satisfaction with specific areas of life (34 questions), while the second section is related to the importance, to the individual, of these same areas of life (34 questions). The 6-point response scale ranges from 1 = very dissatisfied/very unimportant to 6 = very satisfied/very important. Total scores range from 0 to 30, with higher scores indicating better QOL. In this study, Cronbach's alpha values [19] for the QLI were 0.89 (baseline in 1999), 0.97 (first follow-up in 2004), and 0.96 (second follow-up in 2009).
Non-response (35) Benign childhood epilepsy (n=7)
Baseline questionnaire returned (n=151)
5 year follow-up 2004 Non-traceable in the 5-year follow-up 1999 (n=5) Traceable in the 5-year follow-up (n=146)
Completed QLI questionnaire returned (n=102) Completed SOC questionnaire returned (n=97)
10 year follow-up 2009 Non-traceable in the 146 included in 2004 (n=18) Traceable in the 10-year follow-up (n=128) Questionnaire returned (n=87) Completed QLI and SOC questionnaires at all three data collection periods (n=69)
Fig. 1. Flow chart.
The Sense of Coherence (SOC) scale developed by Antonovsky comprises comprehensibility, manageability, and meaningfulness [20]. In this study, the 13-item version [21] was used at all three occasions. The 7-point response scale ranges from 1 to 7, with higher scores representing higher sense of coherence. The total SOC score was calculated by adding each item's score, ranging from 13 to 91, with higher scores representing stronger SOC. In the present study, Cronbach's alpha values were 0.51 (baseline in 1999), 0.89 (first follow-up in 2004), and 0.87 (second follow-up in 2009). In addition, some background and study-specific questions were included in the questionnaire (see Table 1).
2.4. Analysis Statistical analyses were performed using SPSS, version 20.0. Descriptive statistics with frequencies, percent, range, mean, and standard deviation were used to describe the study sample. Estimates of internal consistency were established with Cronbach's alpha [19]. The mean SOC score and mean QLI score from the first (1999), second (2004), and third (2009) data collection points were compared using Friedman's two-way analysis of variance by ranks test and the Wilcoxon signedrank test, while differences between two independent groups were analyzed using the Mann–Whitney U-test [22]. For nonparametric-related samples, McNemar's test was used. The correlation between QLI and SOC was tested with Spearman's rho. The epilepsy diagnoses were categorized based on the ICD-10 codes used in 2004: “focal seizures” (ICD-10 code 40.1 or 40.2); “generalized
M. Persenius et al. / Epilepsy & Behavior 47 (2015) 127–131
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Table 1 Frequency of seizures in 2004 and 2009 by gender. Frequency of seizures
2004
NOnce a week NOnce a month bOnce a month Never/less than once a year Missing
2009
Total (n = 69)
Men (n = 21)
Women (n = 48)
Total (n = 69)
Men (n = 21)
Women (n = 48)
– 3 20 46 –
– – 7 14 –
– 3 13 32 –
1 3 4 45 16
– 1 1 14 5
1 2 3 31 11
seizures” (ICD-10 code 40.3, 40.4, or 40.6); and finally, “seizures not classified” (ICD-10 code 40.8 or 40.9). The classification used to determine how well the epilepsy was controlled was the one designed by Ericsson and Koivikko [23]: good control = no seizures during the last year, partial control = one or more seizures during the last year but not more than one per month, and poor control = more than one seizure per month. Changes in QOL and SOC were calculated as the values at data collection 2 (2004) minus the values at baseline (1999) and the values at data collection 3 (2009) minus the values at data collection 2 (2004). All tests were two-tailed and were assessed at a significance level of p b 0.05. 2.5. Ethical considerations The study was approved by a regional research committee in Sweden (reference numbers 98-312 (1999), 03-532 (2004), and C 2009/253 (2009)). The study was conducted in accordance with the ethical principles of human research [24]. 3. Results The results showed that sixty-nine out of the 158 persons who accepted the invitation at baseline (43.7%) had completed the questionnaires at all three occasions (1999, 2004, and 2009). At the end of the study (2009), 69 of these people were aged between 23 and 33 years (mean: 28.9, SD: 2.78). Forty-eight were females (69.6%) and 21 males (30.4%). At the final follow-up, more than half of the respondents (60.8%) were living in a relationship, that is, married/cohabitating with child(ren) (37.3%), married/cohabitating without child(ren) (20.9%), or living alone (4.5%). Almost one-third (32.8%) were unmarried/cohabiting without child(ren), and 3% were unmarried/cohabitating with child(ren). One person had not yet moved out of the parental home (1.5%). The majority were employed (68.7%), ten were students (14.9%), seven were unemployed (10.4%), and two were on sick leave (3%). Two had other, nonspecified, work conditions (3.0%). Among those
who had employment, it was on either a full-time (49.3%) or parttime (19.4%) basis. A few had other – nonspecified – self-reported dysfunctions (10.4%). Two-thirds had a driving license (66.7%). A total of eight persons still had seizures in 2009 (11.6%) (two men and six women) (see Table 1). This was a significant decrease (p ≤ 0.001) compared to the 2004 results, mainly among the women (p = 0.003). 3.1. QLI and SOC (1999–2009) When comparing the total QLI scores, no significant differences were found between the three data collections (see Table 2) and there were no differences in total scores between men and women. There were no significant associations between QLI and age, civil status, work condition, having a driving license, frequencies of seizures, or type of seizures. Between 2004 and 2009, the total score of sense of coherence (SOC scale) decreased significantly (p = 0.003), which was also the case between 1999 and 2009 (p ≤ 0.001) (Table 2). This decrease included both female (p = 0.040) and male (p = 0.024) respondents between 2004 and 2009. The SOC was significantly higher among those being 30–33 years old compared to those being 23–29 years old (p = 0.014) and among persons with a driving license (p = 0.029) compared to those not having a driving license. There were no significant associations between SOC and civil status, work condition, frequencies of seizures, or type of seizures. There were significant positive correlations (p b 0.001) between SOC and QLI at baseline and at data collection points 2 and 3. The more positive the QLI, the more SOC increased. 4. Discussion To our knowledge, this is the first study to use a 10-year longitudinal design to describe and explore potential changes in quality of life and
Table 2 Quality-of-Life Index (QLI) scores, total and subscales, and total sense of coherence (SOC) for young people with epilepsy in 1999, 2004, and 2009. 1999
QLI Totalc Health and functioning Socioeconomics Psychological/spiritual Family and friends Total SOCd a b c d
2004
p-Valuea
2009
n
Mean
SD
Range
n
Mean
SD
Range
n
Mean
SD
Range
69 69 69 68 69 69
22.16 22.49 22.00 20.85 23.46 64.99
3.74 3.65 4.42 4.94 4.58 13.11
11.7–29.4 12.1–29.0 10.3–30.0 3.5–30.0 11.6–30.0 34–88
69 69 69 68 69 69
22.16 22.13 22.25 20.92 24.86 61.84
3.76 4.05 4.16 5.01 4.42 13.13
11.7–29.4 11.3–29.2 12.8–30.0 3.3–30.0 13.0–30.0 30–87
69 69 68 68 68 69
22.36 22.53 21.83 21.48 24.11 58.82
4.43 4.34 5.04 5.49 6.17 11.64
8.6–29.4 10.2–29.2 7.3–30.0 5.5–30.0 0.0–30.0 31–78
Friedman's two-way analysis of variance by ranks, p-value ≤ 0.05. Wilcoxon signed-rank test (exact sig. 2-tailed), p-value ≤ 0.05. Total scores range from 0 to 30, with high scores indicating better QOL. Total SOC is ranging from 13 to 91, with higher scores indicating stronger SOC.
.784 .173 .755 .585 .020 0.002
5-year follow-up (2004–2009)
10-year follow-up (1999–2009)
p-Valueb
p-Valueb
.846 .435 .359 .262 .644 0.003
.832 .760 .627 .214 .230 b0.001
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sense of coherence in relation to gender in adolescents and adults with uncomplicated epilepsy. The result showed a significant decrease (p ≤ 0.001) in seizures compared with the 2004 results, mainly among the women (p = 0.003). Even though the study focused on uncomplicated epilepsy, it is somewhat surprising to find that the vast majority of the persons were seizure-free after ten years. About 70% of patients with epilepsy experience control of seizures with AEDs according to the WHO [1]. However, in 2009, there were missing responses regarding the participant's seizures, which suggest that the results should be interpreted with caution. The results showed no difference in total QLI scores across the study time periods. When comparing our results with those in a Swedish population of 18- to 30-year-olds where the overall mean score was found to be 21.3 [25], the total QLI score during the entire time period in our study was higher. This finding correlates with those of other studies. Among adolescents with congenital heart disease, the QOL was significantly higher compared with the control group [26]. It has been suggested that QOL and health are two separate constructs, although they are not mutually exclusive [7], something that could explain why persons with epilepsy are reporting high quality of life in spite of being affected by epilepsy. Another explanation could be that persons with disorders that were considered to affect QOL in a substantial way were excluded. In our study, the total score of SOC significantly decreased between 1999 and 2009, which is the period when the persons grew up with epilepsy, from age 13–22 years to age 23–33 years. The research literature is inconsistent regarding whether SOC is stable or changes over time. According to a salutogenic perspective [20], SOC should be relatively stabilized at the end of early adulthood [20], although in a 5-year follow-up study in a general Swedish population, in those aged 25–74 years, SOC was stable only when scores were high from the outset [27]. In our study, SOC was significantly higher among those aged 30–33 years compared to those aged 23–29 years (p = 0.014), indicating a stabilization of SOC that is in line with other studies [20]. Reviewing previous research [28], there have been few studies supporting the notion of a stable SOC throughout the lifespan; in contrast, they observed that it tends to increase with age. When comparing our results with a study in the general population aged 15 to 29 years (62.74) [29], the total SOC score was somewhat higher at baseline in 1999 (64.99). It is known that individuals with stronger SOC tend to cope with their ill health better compared to those with a weaker SOC [20,27]. One-third of the persons did not have a driving license; however, no impact on their QOL was shown despite that it is often cited as a lifestyle limitation [7]. This contradicts other findings where driving significantly affected QOL [12]. Total SOC, however, was significantly lower among persons without a driving license (p = 0.029) compared to persons with a driving license in our study, indicating a level of discontent with the situation. The results showed that SOC is strongly associated with the QLI, a finding well in line with the results from other studies [30]. In addition, SOC has been identified as a determinant of QOL, over time, in female survivors of acute myocardial infarction [31] and an important resource for quality of life among patients with congenital heart disease [26]. The SOC concept is considered to be a health resource influencing QOL [30,31], and it has been suggested that a salutogenic approach in clinical practice, focusing on patient resources and strengths rather than on problems and limitations, could optimize the QOL for people affected by epilepsy [31]. 4.1. Methodological concerns We had a 43% response rate in the 10-year follow-up, indicating that many of the study participants deemed the study to be highly important. With only a few exceptions, the response rates to individual QLI
items were consistent, with a limited number of internally missing data. Regarding SOC, there was one internally missing data point (n = 1) for each data collection time period. The use of well-known and validated instruments may be considered as strength of our study. In this study, Cronbach's alpha values for the QLI were 0.89 (baseline in 1999), 0.97 (first follow-up in 2004), and 0.96 (second follow-up in 2009). The Cronbach's alpha values regarding SOC ranged between 0.70 and 0.92 in 127 studies according to Eriksson and Lindström [30]. Here, in the present study, Cronbach's alpha values were 0.51 (baseline in 1999), 0.89 (first follow-up in 2004), and 0.87 (second follow-up in 2009). 5. Conclusion To our knowledge, our study is the first to report a stable QLI over a ten-year period among persons with uncomplicated epilepsy, during the transition from adolescence to adulthood, while there was a decrease in SOC during the same time period. Both quality of life and sense of coherence are important resources for maintaining health and well-being. Promoting health and wellbeing requires effective high-quality multidisciplinary person-centered care. Health-care professionals have an important role in supporting individuals in their daily lives. Aside from being knowledgeable about QOL and SOC in persons with epilepsy, they should be empowering patients and their relatives through education and psychosocial support and involving them in decision-making regarding their treatment and care. Further areas for research include evaluation of the effect of interventions aimed at enhancing or maintaining health and well-being in persons with epilepsy. Acknowledgment We gratefully thank senior lecturer Lena Räty for the design and planning of this study, lecturer (and research assistant) Maria Bystedt for the data collection, and Professor Jari Appelgren for his statistical advice. Sincere gratitude is also expressed to the persons with epilepsy, the study participants, who made this study possible. Conflict of interest The authors declare they have no competing interest and no financial disclosures. References [1] WHO. Epilepsy. Available at: http://www.who.int/mediacentre/factsheets/fs999/en/ . ; 2012. [retrieved 2014-10-08]. [2] Ben-Menachem E, Olsson I, Uvebrant P. Epilepsy. In: Örtqvist P, editor. Läkemedelsboken Läkemedelsverket; 2014. p. 972–81 [http://www.lakemedelsboken.se/ (retrieved 201404-25)]. [3] Forsgren L, Beghib A, Õun A, Sillanpää M. The epidemiology of epilepsy in Europe — a systematic review. Eur J Neurol 2005;12:245–53 [http://onlinelibrary.wiley.com/ doi/10.1111/j.1468-1331.2004.00992.x/pdf]. [4] World Health organization. Adolescent friendly health services: an agenda for change. Geneva: WHO; 2002[http://www.who.int/maternal_child_adolescent/ documents/fch_cah_02_14/en/ (retrieved 2014-04-25)]. [5] United Nations. http://www.un.org/esa/socdev/documents/youth/fact-sheets/ youth-definition.pdf. [6] Talati R, Scholle JM, Phungh OJ, Baker WL, Baker EL, Ashaye A, et al. Effectiveness and safety of antiepileptic medications in patients with epilepsy. (Internet) Comparative effectiveness reviews, no. 40. Rockville (MD): Agency for Healthcare Research and Quality (US); 2011[http://www.ncbi.nlm.nih.gov/ books/NBK83937/ (retrieved 2014-11-10)]. [7] Jacoby A, Snape D, Baker G. Determinants of quality of life in people with epilepsy. Neurol Clin 2009;27(4):843–63. [8] Benavente-Aguilar I, Morales-Blánquez C, Rubio EA, Rey JM. Quality of life of adolescents suffering from epilepsy living in the community. J Paediatr Child Health 2004; 40:110–3. [9] Räty L, Hamrin E, Söderfeldt B. Quality of life in newly-debuted epilepsy, an empirical study. Acta Neurol Scand 1999;100:221–6.
M. Persenius et al. / Epilepsy & Behavior 47 (2015) 127–131 [10] Witt J-A, Werhahn J, Krämer G, Ruckes C, Trinka E, Helmstaedter C. Cognitive– behavioral screening in elderly patients with new-onset epilepsy before treatment. Acta Neurol Scand 2014;130:172–7. [11] Edefonti V, Bravi F, Turner K, Beghi E, Canevini MP, Ferraroni M, et al. Health-related quality of life in adults with epilepsy: the effect of age, age at onset and duration of epilepsy in a multicenter Italian study. BMC Neurol 2011;11(33) [http://www. biomedcentral.com/1471-2377/11/33 (retrieved 2014-11-14)]. [12] Jehi L, Tesar G, Obuchowski N, Novak E, Najm I. Quality of life in 1931 adult patients with epilepsy: seizures do not tell the whole story. Epilepsy Behav 2011;22:723–7. [13] Auriel E, Landov H, Blatt I, Theitler J, Gandelman-Marton R, Chistik V, et al. Quality of life in seizure-free patients with epilepsy on monotherapy. Epilepsy Behav 2009;14: 130–3. [14] Räty L, Larsson G, Söderfeldt A, Wilde Larsson B. Psychosocial aspects of health in adolescence: the influence of gender, and general self-concepts. J Adolesc Health 2005; 36:530.e21–8. [15] Räty L, Wilde-Larsson B, Söderfeldt B. Health-related quality of life in youth: a comparison between adolescents and young adults with uncomplicated epilepsy and healthy controls. J Adolesc Health 2003;33:252–8. [16] Räty L, Wilde-Larsson B. Quality of life in young adults with uncomplicated epilepsy. Epilepsy Behav 2007:142–7. [17] Gauffin H, Landtblom A-M, Räty L. Self-esteem and sense of coherence in young people with uncomplicated epilepsy: a 5-year follow-up. Epilepsy Behav 2010;17: 520–4. [18] Ferrans CE, Powers MJ. Psychometric assessment of the quality of life index. Res Nurs Health 1992;15:29–38. [19] Cronbach L. Coefficient alpha and the internal structure of tests. Psychometrika 1951;16:297–334. [20] Antonovsky A. The structure and properties of the sense of coherence scale. Soc Sci Med 1993;36(6):725–33. [21] Guldvog B. Spørsmål om livet. Aron Antonovsky's sence of coherence scale. Sentralsykehuset I Akershus: Stiftelsen for Helsetjenste forskning; 1996 (in Norwegian).
131
[22] Polit DF, Beck CT, editors. Nursing research: generating and assessing evidence for nursing practice. 9th ed. Philadelphia: Lippincott Williams and Wilkins; 2012. [23] Ericsson KJ, Koivikko MJ. Prevalence, classification and severity of epilepsy and epileptic syndromes in children. Epilepsia 1997;38(12):1275–82. [24] Northern Nurses Federation. Ethical guidelines for nursing research in the Nordic countries. Vard Nord Utveckl Forsk Nord J Nurs Res 2003;23(4):1–19. [25] Gullberg MT, Hollman-Frisman G, Ek A-K. Reference values for the Quality of Life Index in the general Swedish population 18–80 years of age. Qual Life Res 2010; 19:751–60. [26] Apers S, Luykx K, Rassart J, Goossens E, Budts W, Moons P. Sense of coherence is a predictor of perceived health in adolescents with congenital heart disease: a crosslagged prospective study. Int J Nurs Stud 2013;50:776–85. [27] Nilsson B, Holmgren L, Stegmayr B, Westman G. Sense of coherence — stability over time and relation to health, disease, and psychosocial changes in a general population: a longitudinal study. Scand J Public Health 2003;31:297–304. [28] Eriksson M, Lindström B. Validity of Antonovsky's sense of coherence scale: a systematic review. J Epidemiol Community Health 2005;59:460–6. http://dx.doi. org/10.1136/jech.2003.018085. [29] Larsson G, Kallenberg K-O. Sense of coherence, socioeconomic conditions and health. Interrelationships in a nation-wide Swedish sample. J Public Health 1996; 6:175–80. [30] Eriksson M, Lindström B. Antonovsky's sense of coherence scale and its relation with quality of life: a systematic review. J Epidemiol Community Health 2007;61:938–44. http://dx.doi.org/10.1136/jech.2006.056028. [31] Norekvål TM, Fridlund B, Moons P, Nordrehaug JE, Saevareid HI, Wentzel-Larsen T, et al. Sense of coherence a determinant of quality of life over time in older female acute myocardial infarction survivors. J Clin Nurs 2009;19:820–31. http://dx.doi. org/10.1111/j.1365-2702.2009.02858.x.