Internal consistency of the self-reporting questionnaire-20 in occupational groups

Santos, Kionna Oliveira Bernardes; Carvalho, Fernando Martins; Araújo, Tânia Maria de

doi:10.1590/S1518-8787.2016050006100

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Original Articles • Rev. Saúde Pública 50 • 2016 • https://doi.org/10.1590/S1518-8787.2016050006100 copy

Internal consistency of the self-reporting questionnaire-20 in occupational groups

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

OBJECTIVE

To assess the internal consistency of the measurements of the Self-Reporting Questionnaire (SRQ-20) in different occupational groups.

METHODS

A validation study was conducted with data from four surveys with groups of workers, using similar methods. A total of 9,959 workers were studied. In all surveys, the common mental disorders were assessed via SRQ-20. The internal consistency considered the items belonging to dimensions extracted by tetrachoric factor analysis for each study. Item homogeneity assessment compared estimates of Cronbach’s alpha (KD-20), the alpha applied to a tetrachoric correlation matrix and stratified Cronbach’s alpha.

RESULTS

The SRQ-20 dimensions showed adequate values, considering the reference parameters. The internal consistency of the instrument items, assessed by stratified Cronbach’s alpha, was high (> 0.80) in the four studies.

CONCLUSIONS

The SRQ-20 showed good internal consistency in the professional categories evaluated. However, there is still a need for studies using alternative methods and additional information able to refine the accuracy of latent variable measurement instruments, as in the case of common mental disorders.

Mental Health; Questionnaires, utilization; Reproducibility of Results; Validation Studies; Mental Disorders, diagnosis; Workers

Study - Population (N)		n	%
Study 1 – Informal workers (N = 1,458)
Sex	Female	728	49.9
	Male	730	50.1
Age group (years)	< 30	537	36.8
	30-45	553	37.9
	> 45	368	25.2
Educational attainment (n = 1,438)	Less than primary education	1,379	95.9
	Secondary technical education/Higher education	9	0.6
	No qualification	50	3.5
Study 2 – Teachers (N = 4,496)
Sex (n = 4,342)	Female	3,994	92.0
	Male	348	8.0
Age group (years) (n = 4,302)	< 30	773	18.0
	30-45	2,289	53.2
	> 45	1,240	28.8
Educational attainment (n = 4,398)	Less than primary education	717	16.3
	Secondary technical education/Higher education	3,609	82.1
	Graduate education	72	1.6
Study 3 – Health care workers (N = 2,448)
Sex (n = 2,421)	Female	1,951	80.6
	Male	470	19.4
Age group (years) (n = 2,395)	< 30	581	24.3
	30-45	1,071	44.7
	> 45	743	31.0
Educational attainment (n = 2,419)	Less than primary education	1,038	42.9
	Secondary technical education/Higher education	1,000	41.3
	Graduate education	381	15.8
Study 4 – Urban workers (N = 1,557)
Sex	Female	851	54.7
	Male	706	45.3
Age group (years)	< 30	576	37.0
	30-45	584	37.5
	> 45	397	25.5
Educational attainment (n = 1,269)	Less than primary education	536	42.3
	Secondary technical education/Higher education	710	55.9
	No qualification	23	1.8

	Group of workers

	Informal workers		Teachers		Health care workers		Urban workers

	(n = 1,453)^a		(n = 3,891)^b		(n = 2,397)^c		(n = 1,539)^d

SRQ-20 items	α1^e	α2^f	α1^e	α2^f	α1^e	α2^f	α1^e	α2^f
1. Do you often have headaches?	0.85	0.93	0.85	0.93	0.82	0.92	0.84	0.92
2. Is your appetite poor?	0.84	0.93	0.85	0.93	0.82	0.92	0.83	0.92
3. Do you sleep badly?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92
4. Are you easily frightened?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92
5. Do your hands shake?	0.84	0.93	0.85	0.93	0.81	0.91	0.84	0.92
6. Do you feel nervous, tense or worried?	0.84	0.93	0.84	0.93	0.80	0.91	0.83	0.92
7. Is your digestion poor?	0.84	0.92	0.85	0.93	0.81	0.91	0.84	0.92
8. Do you have trouble thinking clearly?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92
9. Do you feel unhappy?	0.84	0.92	0.84	0.93	0.80	0.90	0.83	0.92
10. Do you cry more than usual?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92
11. Do you find it difficult to enjoy your daily activities?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92
12. Do you find it difficult to make decisions?	0.84	0.93	0.85	0.93	0.81	0.91	0.84	0.92
13. Is your daily work suffering?	0.84	0.93	0.85	0.93	0.82	0.91	0.84	0.92
14. Are you unable to play a useful part in life?	0.85	0.93	0.86	0.94	0.82	0.92	0.83	0.92
15. Have you lost interest in things?	0.84	0.92	0.85	0.93	0.81	0.91	0.83	0.92
16. Do you feel that you are a worthless person?	0.85	0.93	0.86	0.93	0.82	0.92	0.84	0.92
17. Has the thought of ending your life been on your mind?	0.85	0.93	0.86	0.94	0.82	0.91	0.84	0.92
18. Do you feel tired all the time?	0.84	0.93	0.84	0.93	0.81	0.91	0.83	0.92
19. Do you have uncomfortable feelings in your stomach?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92
20. Are you easily tired?	0.84	0.93	0.85	0.93	0.81	0.91	0.83	0.92

Total	0.85	0.94	0.85	0.94	0.82	0.92	0.84	0.93

Study - Population (N)	Items (N)	Losses	Cronbach’s alpha	Cronbach’s alpha (Tetrachoric)
Study 1 – Informal workers (N = 1,453)
F1 - Depressive mood/Anxiety symptoms	11	5	0.79	0.90
F2 - Somatic component	5	0	0.65	0.79
F3 - Decreased energy	4	0	0.65	0.76
Scale total	20	5	0.85	0.92
Stratified Cronbach’s alpha	-	-	0.86	0.93
Study 2 – Teachers (N = 3,891)
F1 - Decreased energy/Anxiety symptoms	11	434	0.82	0.92
F2 - Somatic component	6	295	0.68	0.82
F3 - Depressive mood	3	242	0.41	0.74
Scale total	20	605	0.85	0.93
Stratified Cronbach’s alpha	-	-	0.82	0.94
Study 3 – Health care workers (N = 2,397)
F1 - Depressive mood	9	33	0.67	0.87
F2 - Decreased energy/Anxiety symptoms	9	44	0.72	0.87
F3 - Somatic component	2	17	0.70	0.87
Scale total	20	60	0.82	0.92
Stratified Cronbach’s alpha	-	-	0.83	0.93
Study 4 – Urban workers (N = 1,539)
F1 - Somatic component/Anxiety symptoms	11	8	0.78	0.88
F2 - Decreased energy	5	6	0.62	0.82
F3 - Depressive mood	4	4	0.64	0.86
Scale total	20	18	0.84	0.93
Stratified Cronbach’s alpha	-	-	0.85	0.93

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[1] Correspondence: Kionna Oliveira Bernardes Santos. Av. Miguel Calmon, s/n Vale do Canela 40110-100 Salvador, BA, Brasil. E-mail:kionna.bernardes@ufba.br