Heart Mind

ORIGINAL ARTICLE
Year
: 2019  |  Volume : 3  |  Issue : 1  |  Page : 15--20

Prevalence rates of chronic fatigue complaints in a probability sample of Arab college students


Ahmed M Abdel-Khalek 
 Department of Psychology, Faculty of Arts, Alexandria University, Alexandria, Egypt

Correspondence Address:
Dr. Ahmed M Abdel-Khalek
Department of Psychology, Faculty of Arts, Alexandria University, Alexandria
Egypt

Abstract

Objectives: Fatigue is a common complaint in the community. The twofold aims of the present study were (a) to estimate the prevalence rate of reported chronic fatigue syndrome-like (CFS-like) complains, and (b) to explore the sex-related differences in it. Methods: A probability non-clinical sample of 3,465 Kuwaiti volunteer undergraduate men (n = 1,745) and women (n = 1,720) was recruited. Their ages ranged between 16 and 43 years. They responded to the Arabic Scale of Chronic Fatigue (ASCF). It has good internal consistency, temporal stability, criterion-related validity, and factorial validity (its loading on a CFS factor = 0.81). Principal component analysis disclosed 2 factors: Mental fatigue and Physical fatigue. The prevalence rate was computed based on 2 criteria, i.e., the percentage of persons which have total scores greater than (a) the M + 1 SD, and (b) greater than the M + 2 SD. Results: Based on criterion (a), prevalence rates were 13.47% for men and 20.98% for women. As to criterion (b), the rates were 2.35% for men and 5.76 % for women. These rates lie in the rage of the international studies on CFS-like complaints (from 1.2% to 30.5%). Women obtained significantly higher mean score and prevalence rates than did their male counterparts. Conclusion: It is highly probable that the participants obtained the higher scores than did their M + 2 SD are in need of therapeutic intervention. It was concluded that psychological scales may be useful in screening disorders to detect the cases.



How to cite this article:
Abdel-Khalek AM. Prevalence rates of chronic fatigue complaints in a probability sample of Arab college students.Heart Mind 2019;3:15-20


How to cite this URL:
Abdel-Khalek AM. Prevalence rates of chronic fatigue complaints in a probability sample of Arab college students. Heart Mind [serial online] 2019 [cited 2022 Nov 27 ];3:15-20
Available from: http://www.heartmindjournal.org/text.asp?2019/3/1/15/270771


Full Text

 Introduction



Every person has experienced fatigue in any part of his or her life. It is essentially a subjective experience and is difficult to separate from normal experiences of tiredness, sleepiness, overstrain, or exercise exhaustion. Further, fatigue is one of the most prevalent symptoms in most countries. It is a ubiquitous and omnipresent symptom in almost all the countries and many patients.

In an Arabic study, the Somatic Symptoms Inventory contained 60 symptoms and complaints,[1],[2] was administered to a nonclinical sample of 1889 (16–60 years) male and female Arab participants. Prevalence rates were computed based on the percentage of the participant's responses to the alternatives: much and always. It was found that the first highest complaint was “Easy fatigability” among men (32.7%), women (44.7%), and the whole sample (38.8%). The critical ratio was 5.37 (P < 0.001).

Fatigue is a common symptom in the community, with up to half of the general population reporting fatigue in large surveys.[3] It is also reported by at least 20% of patients seeking medical care.[4] Fatigue may be considered either a normal experience or symptom. As a symptom, its causes are protean and include physical, psychological, behavioral social, and environmental components.

In the general population, many persons report their feeling of fatigue in some life stage or another. In the same vein, reported fatigue is a common complaint in many patients in hospital settings as well. However, there are differences between normal or prolonged fatigue, chronic fatigue (CF), and CF syndrome (CFS). The boundaries between the last-mentioned terms are arbitrary.[5] Prolonged fatigue is often defined as disabling fatigue that lasts at least 1 month. This is called CF if it is persisting and lasts more than 6 months. CFS must fulfill specific criteria or case definition.[6] Similarly, Wessely et al.[7] stated that fatigue should be considered abnormal when the person sees that he or she to be ill, as well as the decision to seek help, chronicity, and functional impairment. To qualify fatigue as pathological, many researchers have described the subjective experience of fatigue as a continuum rather than a categorical entity.[8]

CFS or myalgic encephalomyelitis (ME) or more recently in the USA, systemic exertion intolerance disease is part of a large group of functional somatic syndromes. It is a chronic multifaceted condition. The WHO [9] International Classification of Diseases 11 named it as postviral fatigue syndrome, included both benign ME and CFS. CFS is characterized by the presence of several disabling medically unexplained mental and physical fatigue of 6 months or more duration. The important question here is: how can clinicians differentiate between “normal” or nonclinical fatigue, CF. and CFS?

There are several diagnostic criteria for CFS. The American Centers for Disease Control and Prevention (CDC)[10] defined CFS criteria as follows: (A) Severe CF, and (B) At least four of the following symptoms: (1) substantial impairment in short-term memory or concentration; (2) headaches of a new type, pattern, or severity; (3) tender lymph nodes; (4) unrefreshing sleep; (5) postexertional malaise lasting more than 24 h; (6) muscle pain; (7) pain in the joints without swelling or redness; and (8) a sore throat that is frequent or recurring.

This pathological fatigue is not relieved or improved by rest and results in a substantial reduction in the patient's activity levels before onset. The afflicted people may experience significant disability, and some may become homebound and bedbound. The CDC case definition appeared to be the most reliable clinical assessment tool available.[11] It is most commonly used as diagnostic criteria when recruiting CFS patients for scientific studies.[12] The etiology and pathogenesis remain unknown, there are no laboratory diagnostic tests; and there are no known cures.[13]

There are other diagnostic criteria of CFS/ME, among them are the Oxford criteria which focuses mainly on mental rather than somatic fatigue. The Canadian criteria expand the CFS/ME definition with additional diagnostic criteria, i.e., postexertional malaise and the presence of neurological, endocrine, cognitive, and autonomic disorders.[12]

Several research studies reported different prevalence rates of CFS and CFS-like complaints. As for the CFS, the worldwide prevalence ranges from 0.2% to 2.7% based on various epidemiological studies.[14],[15],[16],[17] Other epidemiological studies indicate a prevalence of CFS between 0.2% and 0.7% in the general population in Europe, Australia, and USA.[7],[18] Other studies indicated that the prevalence of CFS varies from 0.004% to 2.54% in the community, and from 0.11% to 2.6% in primary care.[19] More recently, Johnston et al.[11] stated that prevalence rates vary from as low as 0.2% to as high as 6.41%. Fukuda et al.[20] estimate for the prevalence of current CFS ranges from 0.007% to 2.8% in the general adult population.

Allowing for psychiatric comorbidity, the prevalence of CFS has been shown to be 2.5%.[21] The CDC conducted a community-based survey in San Fransisco using 14,627 participants by telephone interview. A group of 4.3% reported CF. Following the exclusion of the cases of medical and psychiatric that could explain fatigue, the researchers identified a group of 1.8% as having idiopathic CF.[22]

Jason et al.[15] carried out a community-based study in Chicago, Illinois, involved a random sample of 18,675 individuals. They found a 0.42% CFS prevalence rate and found that women and individuals within a 40–49 age range had the highest CFS rates. A USA community-based study of CFS among 33,997 households found a CFS rate of 0.42%.[16] A Chinese study reported a CFS prevalence of 6.4%.[23] In the UK, prevalence is estimated to be 0.2% to 0.4%.[24] Studies using broader screening assessment tools have found prevalence estimates of over 2%.[25]

Son [26] stated that the prevalence of CFS was very wide from 0.0004% in Australia to 3.6% in the USA. The total average of prevalence for CFS from 24 research papers was 1.2%. The CFS prevalence in women was higher by 3–4-fold than that of men. A meta-analysis of studies based on clinically-confirmed cases in several countries indicated a prevalence of 0.76% (95% confidence interval [CI] 0.23%–1.29%), whereas the pooled prevalence for self-reporting assessment was 3.28% (95% CI: 2.24–4.33).[11] More recently, Słomko et al.[12] in Poland, found that of the cohort of 1400 who self-presented with fatigue only 69 subsequently were confirmed as having CFS/ME using the Fukuda criteria, i.e., 4.9%.

[Table 1] summarizes the prevalence rates of CFS based on previous studies. Inspection of this table indicates that prevalence rates of CFS ranged from 0.0004% to 6.4%.{Table 1}

Regarding the epidemiology of CFS-like complaints, again, different studies indicated different results. For example, using data from the Epidemiological Catchment Area study, Cathébras et al.[27] found that 1-month prevalence of unexplained fatigue lasting longer than 2 weeks of 6%. Pawlikowska et al.[3] carried out a postal survey in the UK. They found that 18.3% of the respondents reported substantial fatigue lasting 6 months or longer and 1.4% attributed it to CFS.

A large community survey of psychiatric morbidity in the UK indicated that 27% of all adults (a third of all women and a fifth of all men) reported significant fatigue in the week before the interview.[28] A 1.5% CFS-like prevalence rate was found in epidemiologic studies in Japan [29] and the same percentage was found in Australia.[30] Skapinakis et al.[31] used a structured interview and found that point prevalence of CF was 13.4%, and that of unexplained CF was 9% in a UK survey.

In Iceland, the prevalence rate of CFS-like was 1.4%.[32] A USA national sample (n = 7317) found a 1.2% CFS-like prevalence rate.[33] A study on CF (not CFS) among Indian women to be as high as 2%.[34] Studies with samples varying in ethnicity, age, gender, and occupational status have shown a high prevalence of CFS reaching 11%–12% from the UK [20] to India.[5] In a representative sample of the German population (n = 2414), the prevalence rate of CF was 6.1%. Females were affected significantly more often as compared with males (7% vs. 5.1%).[35]

As for (CF; not CFS), Jason et al.[36] found the lowest CF prevalence as 4.17% in the USA, whereas van't Leven et al.[37] showed the highest CF prevalence as 30.5% in the Netherlands. The average prevalence of CF from 13 research papers was 11.1%.[26]

[Table 2] summarizes previous studies on CFS-like prevalence rates. Reference to this table reveals that prevalence rates of CFS-like ranged between 1.2% and 30.5%.{Table 2}

The majority of studies on CFS have been carried out on Western-industrialized countries. A limited number of research studies using Arab participants in CFS research domain was published.[38],[39],[40],[41],[42],[43] Hence, the Arab samples are under-studied and under-represented population in this field. Therefore, studies on populations from other countries are highly needed to run cross-cultural comparisons.

The two-fold aims of the present investigation were as follows: (a) to estimate the prevalence rate of reported CFS-like complaints among a nonclinical sample of Arab college students using a questionnaire and (b) to explore the sex-related difference in CFS-like complaints.

 Methods



Participants

A probability nonclinical sample of 3465 volunteer nonpaid Kuwaiti undergraduate men (n = 1745) and women (n = 1720) took part in this study. Their ages ranged between 16 and 43 years. As the present study was a community survey of college students, no information about other medical or psychological investigations was collected.

These participants, as a whole, were neither disturbed clinical cases nor diagnosed institutionalized patients but rather, were presumably healthy individuals. No psychiatric or psychological assessment was conducted.

The Arabic Scale of Chronic Fatigue

This scale was developed by Abdel-Khalek and Al-Theeb.[41] Based on both the previous measures and the experience of its authors, the item pool of the Arabic Scale of CF (ASCF) was constructed. Seven staff members who held doctorate assessed each item for both face or content validity and accuracy of expression. The item-remainder correlation and the correlation with the World Health Organization [44] diagnostic criteria for CFS yielded 20 items which were to be answered on a 5-point Likert scale, anchored by 1 = Not at all and 5 = Very much. Scores could range from 20 to 100, with higher scores indicating higher levels of CF. Its alpha reliability was 0.95, test–retest reliability was 0.88, criterion-related validity (3 criteria) was >0.5, and factorial validity was >0.81. The factor analysis of the 20 items of the ASCF yielded two salient factors: mental fatigue and physical fatigue. The ASCF has two comparable Arabic and English versions.

Procedure

The ASCF, along with other personality questionnaires, were administered anonymously to students in groups of 30–40 students in their classrooms during the university hours. They volunteered for the study after explaining briefly its purpose and assured them of anonymity. Any student can leave if he or she did not want to share with the study. The percentage of participation was 96%. Several qualified research assistants carried out the administration.

Statistical analysis

All the computations in the present investigation depended on the total score on the ASCF 20 items. Frequency tables for men and women were separately computed. The prevalence rate was estimated on the basis of two criteria: (a) M + 1 standard deviation (SD) and (b) M + 2 SD That is, the number of persons which obtained scores greater than the M plus 1 SD and M plus 2 SD, respectively, in men and women, separately Then, the percentages were computed. These two criteria represent the CFS-like prevalence rates at two levels. Mean (M), SD, t- test, and d for effect size were used to test the sex-related difference in the ASCF.

 Results



[Figure 1] presents the histogram of the total scores on the ASCF based on the percentiles.{Figure 1}

[Figure 2] depicts the frequency curve of the total scores on the ASCF based on the percentiles.{Figure 2}

[Table 3] depicts the prevalence rates of the CFS-like among men and women based on two criteria.{Table 3}

Reference to [Table 3], women obtained higher prevalence rates on two criteria than did their male peers.

[Table 4] presents the descriptive statistics and the difference between men and women in the ASCF total score.{Table 4}

As can be seen in [Table 4], women obtained a statistically higher mean CFS-like score than did their male counterparts. While the t value was highly significant, the effect size d was small, because of the large size of the sample.

 Discussion



Fatigue as a personal experience is a common complaint in the community. Based on its duration, there is an important differentiation between fatigue as a transient normal state, prolonged complaint, CF <6 months, and CFS based on specific criteria and lasted for 6 months or more. Because the present investigation recruited a nonclinical sample of undergraduates without applying the CFS diagnostic criteria, this study deals with CF or CFS-like complaints or symptoms and not CFS.

Previous studies indicated a wide range of CFS prevalence rates in different countries, i.e., ranged from 0.0004% to 6.4% [Table 1]. On the other hand, the range of prevalence rates of the CFS-like complaints in previous studies was wider, i.e., from 1.2% to 30.5% [Table 2].

As for the present results on Arab non-clinical undergraduates, the prevalence rates were computed at two levels: (a) M + 1 SD, i.e., 13.47% for men and 20.98% for women, and (b) M + 2 SD, i.e., 2.35% for men and 5.76% for women. It is clear that the prevalence rates of the CFS-like complaints in the present sample lie in the range of international studies. The important question here is as follows: What are the reasons for this wide range of prevalence rates?

Different causes may have impact on CFS and CFS-like complaints. Among these causes, the physical, psychological, behavioral, occupational, environmental, and social factors may have a salient effect on the afflicted person, among other factors. In addition, different studies used different methodological procedures as to the selection of cases or participants, the psychometric tools, the method of approaching the case (face to face, postal survey or mailed questionnaire, telephone talk, etc.), and the personal characteristics of the participants, such as their scores on anxiety and depression, and their test-taking attitudes, mainly the social desirability.

Similarly, different studies used different statistical methods to compute the prevalence rates. Some researchers compute the percentage of the scale scores higher than 1 SD plus the M, whereas others used 2 SDs, others used the percentiles (p) (p 75, p90, orp95). As to the psychometric scales, some researchers used the cutoff-point at the level of the alternative: much, whereas other researchers used the alternative: always or very much. Therefore, it is important to agree on a unified procedure.

As to the sex-related differences in CFS-like complaints, the present results indicated significant differences in favor of women. This result was applied to the difference between the two mean scale scores of men and women (the t-value), the M + 1 SD, and the M + 2 SD criteria. The higher score of CFS-like among women than their male counterparts is congruent with previous studies.[15],[26],[28],[35],[45] This result on CFS may be related to the high scores of women than men on anxiety, depression, and neuroticism.[46],[47],[48]

 Conclusion



With a large nonclinical sample of Arab undergraduates, it was found that the prevalence rate of CFS-like complaints lie in the range of the results of international studies. Furthermore, the mean scale scores and the prevalence rates of CFS-like complaints among women were higher than that of men which is consistent with previous studies. It is highly probable that the persons obtained the higher score than the M + 2 SD are in need of counseling or therapeutic intervention inasmuch as they most probably have proper CFS. This refers to the importance of questionnaires and psychological tools in screening for the high scorers in any psychological disorder. By and large, the screening of mental disorders, including CFS, is important to reach the cases who need psychotherapeutic intervention. This procedure may contribute to the achievement of better productivity and mental health for those participants.

Because the Arab samples are under-studied and under-represented population in the international literature, it is suggested to extend these studies with a probability sample from the general population using other assessment tools. Further, it is suggested to develop a counseling program to ameliorate mental health among participants with high scores on CFS. These are subjects for future investigation.

Limitations

The results of the current investigation must be viewed within the limitations imposed by the data. Foremost among them is the special characteristics of the sample as undergraduates with a limited age range, and probably higher intelligence and education than the general population. As to the psychometric questionnaire, notwithstanding its good reliability and validity, it is always subject to test-taking attitudes, particularly responding based on social desirability. However, the anonymous administration of the scale may reduce this effect.

Acknowledgment

The author would like to thank the participants for their effort and time and the research assistants for helping in the collection of data.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1Abdel-Khalek AM. The somatic symptoms inventory (SSI): Development, parameters, and correlates. Curr Psychiatry (Egypt)2003;10:114-29.
2Abdel-Khalek AM. Prevalence rates of physical symptoms in a Kuwaiti sample. Derasat Nafseyah (Psychol Stud) 2009a;19:673-89.
3Pawlikowska T, Chalder T, Hirsch SR, Wallace P, Wright DJ, Wessely SC, et al. Population based study of fatigue and psychological distress. BMJ 1994;308:763-6.
4Bates DW, Schmitt W, Buchwald D, Ware NC, Lee J, Thoyer E, et al. Prevalence of fatigue and chronic fatigue syndrome in a primary care practice. Arch Intern Med 1993;153:2759-65.
5Ranjith G. Epidemiology of chronic fatigue syndrome. Occup Med (Lond) 2005;55:13-9.
6Mulrow CD, Ramirez G, Cornell JE, Allsup K. Defining and managing chronic fatigue syndrome. Evid Rep Technol Assess (Summ) 2001;42:1-4.
7Wessely S, Hotopf M, Sharpe M. Chronic Fatigue and its Syndromes. Oxford: Oxford University Press; 1998.
8Sharpe M. The symptom of generalized fatigue. Pract Neurol 2006;6:72-7.
9World Health Organization. The International Classification of Diseases: Mortality and Morbidity Statistics (11th revision). Geneva: World Health Organization; 2018.
10Fukuda K, Straus SE, Hickie I, Sharpe MC, Dobbins JG, Komaroff A. The chronic fatigue syndrome: A comprehensive approach to its definition and study. International chronic fatigue syndrome study group. Ann Intern Med 1994;121:953-9.
11Johnston S, Brenu EW, Staines D, Marshall-Gradisnik S. The prevalence of chronic fatigue syndrome/myalgic encephalomyelitis: A meta-analysis. Clin Epidemiol 2013;5:105-10.
12Słomko J, Newton JL, Kujawski S, Tafil-Klawe M, Klawe J, Staines D, et al. Prevalence and characteristics of chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) in Poland: A cross-sectional study. BMJ Open 2019;9:e023955.
13Green CR, Cowan P, Elk R, O'Neil KM, Rasmussen AL. Advancing the research on Myalgic encephalomyelitis/chronic fatigue syndrome. National Institutes of Health, Executive Summary; December, 2014.
14Jason LA, Taylor R, Wagner L, Holden J, Ferrari JR, Plioplys AV, et al. Estimating rates of chronic fatigue syndrome from a community-based sample: A pilot study. Am J Community Psychol 1995;23:557-68.
15Jason LA, Richman JA, Rademaker AW, Jordan KM, Plioplys AV, Taylor RR, et al. A community-based study of chronic fatigue syndrome. Arch Intern Med 1999;159:2129-37.
16Lawrie SM, Manders DN, Geddes JR, Pelosi AJ. A population-based incidence study of chronic fatigue. Psychol Med 1997;27:343-53.
17Reyes M, Nisenbaum R, Hoaglin DC, Unger ER, Emmons C, Randall B, et al. Prevalence and incidence of chronic fatigue syndrome in Wichita, Kansas. Arch Intern Med 2003;163:1530-6.
18Maquet D, Demoulin C, Crielaard JM. Chronic fatigue syndrome: A systematic review. Ann Readapt Med Phys 2006;49:337-47, 418-27.
19Cho HJ, Menezes PR, Hotopf M, Bhugra D, Wessely S. Comparative epidemiology of chronic fatigue syndrome in Brazilian and British primary care: Prevalence and recognition. Br J Psychiatry 2009;194:117-22.
20Fukuda K, Dobbins JG, Wilson LJ, Dunn RA, Wilcox K, Smallwood D. An epidemiologic study of fatigue with relevance for the chronic fatigue syndrome. J Psychiatr Res 1997;31:19-29.
21Wessely S, Chalder T, Hirsch S, Wallace P, Wright D. The prevalence and morbidity of chronic fatigue and chronic fatigue syndrome: A prospective primary care study. Am J Public Health 1997;87:1449-55.
22Steele L, Dobbins JG, Fukuda K, Reyes M, Randall B, Koppelman M, et al. The epidemiology of chronic fatigue in San Francisco. Am J Med 1998;105:83S-90S.
23Yiu YM, Qiu MY. A preliminary epidemiological study and discussion on traditional Chinese medicine pathogenesis of chronic fatigue syndrome in Hong Kong. Zhong Xi Yi Jie He Xue Bao 2005;3:359-62.
24National Institute of Health and Care Excellence. Chronic Fatigue Syndrome/Myalgic Encephalomyelitis; 2007. Available from: http://www.nice.org.uk/nicemedia/live/11824/36193/39163. [Last retrieved on 2019 Jan 20].
25Reeves WC, Jones JF, Maloney E, Heim C, Hoaglin DC, Boneva RS, et al. Prevalence of chronic fatigue syndrome in metropolitan, urban, and rural Georgia. Popul Health Metr 2007;5:5.
26Son CG. Review of the prevalence of chronic fatigue worldwide. J Korean Oriental Med 2012;33:25-33.
27Cathébras PJ, Robbins JM, Kirmayer LJ, Hayton BC. Fatigue in primary care: Prevalence, psychiatric comorbidity, illness behavior, and outcome. J Gen Intern Med 1992;7:276-86.
28Meltzer H, Gill D, Petticrew M, Hinds K. The Prevalence of Psychiatric Morbidity among Adults Living in Private Households. London: HMSO; 1995.
29Kawakami N, Iwata N, Fujihara S, Kitamura T. Prevalence of chronic fatigue syndrome in a community population in Japan. Tohoku J Exp Med 1998;186:33-41.
30Hickie I, Davenport T, Issakidis C, Andrews G. Neurasthenia: Prevalence, disability and health care characteristics in the Australian community. Br J Psychiatry 2002;181:56-61.
31Skapinakis P, Lewis G, Meltzer H. Clarifying the relationship between unexplained chronic fatigue and psychiatric morbidity: Results from a community survey in Great Britain. Int Rev Psychiatry 2003;15:57-64.
32Líndal E, Stefánsson JG, Bergmann S. The prevalence of chronic fatigue syndrome in Iceland – A national comparison by gender drawing on four different criteria. Nord J Psychiatry 2002;56:273-7.
33Bierl C, Nisenbaum R, Hoaglin DC, Randall B, Jones AB, Unger ER, et al. Regional distribution of fatiguing illnesses in the United States: A pilot study. Popul Health Metr 2004;2:1.
34Patel V, Kirkwood BR, Weiss H, Pednekar S, Fernandes J, Pereira B, et al. Chronic fatigue in developing countries: Population based survey of women in India. BMJ 2005;330:1190.
35Martin A, Chalder T, Rief W, Braehler E. The relationship between chronic fatigue and somatization syndrome: A general population survey. J Psychosom Res 2007;63:147-56.
36Jason LA, Jordan KM, Richman JA, Rademaker AW, Huang CF, McCready W, et al. A community-based study of prolonged fatigue and chronic fatigue. J Health Psychol 1999;4:9-26.
37van't Leven M, Zielhuis GA, van der Meer JW, Verbeek AL, Bleijenberg G. Fatigue and chronic fatigue syndrome-like complaints in the general population. Eur J Public Health 2010;20:251-7.
38Abdel-Khalek AM. Chronic fatigue, affective disorders and psychopathology among Kuwaiti students. The 4th Biennial Conference of the International Society for Affective Disorders. Cape Town, South Africa; 2008. p. 14-7.
39Abdel-Khalek AM. The relation between insomnia and chronic fatigue among a non-clinical sample using questionnaires. Sleep Hypnosis 2009b; 11:9-17.
40Abdel-Khalek AM. The relationship between fatigue and personality in a student population. Soc Behav Personality 2009c; 37:1357-68.
41Abdel-Khalek AM, Al-Theeb SA. The construction and validation of the Arabic Scale of Chronic Fatigue. Derasat Nafseyah (Psychol Stud) 2006;16:525-36.
42Abdel-Khalek AM, Al-Theeb SA. Chronic fatigue and its relation with self-esteem and satisfaction with life. Arabic Stud Psychol 2007;6:93-147.
43Al-Theeb SA, Abdel-Khalek AM. Chronic fatigue syndrome and its relationship to anxiety and depression among a sample of Kuwait University students. Derasat Nafseyah (Psychol Stud) 2006;16:113-35.
44World Health Organization. The ICD-10 Classification of Mental and Behavioral Disorders: Diagnosis and Criteria for Research. Geneva: World Health Organization; 1993.
45Faro M, Sàez-Francás N, Castro-Marrero J, Aliste L, de Sevilla TF, Alegre J. Gender differences in chronic fatigue syndrome. Reumatol Clin 2015;12:72-7.
46Abdel-Khalek AM. Constructions of anxiety and dimensional personality model among college students. Psychol Rep 2013;112:992-1004.
47Abdel-Khalek AM. Sex differences in personality dimensions in an Egyptian sample. Mankind Q 2018;58:588-98.
48Nolen-Hoeksema S. Gender differences in depression. Curr Dir Psychol Sci 2001;10:173-6.