2005, Number 1
Data about validity and reliability of the Symptom Check List 90 (SCL 90) in a Mexican population sample.
Cruz FCS, López BL, Blas GC, González ML, Chávez BRA
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Language: Spanish
References: 19
Page: 72-81
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ABSTRACT
A genetic epidemiology paradigm employed in the identification of genes associated with a disease depends on the comparison of the frequency of common genetic variants between groups of individuals who possess a relevant trait versus those who do not show the trait (i.e., cases vs. controls genetic association study). The adequate classification of groups of contrast is therefore of seminal importance for the identification of relevant genes. For psychiatric disorders, the careful clinical evaluation of particular symptoms is the basis for the classification of the “affected or disease group”. However, in many psychiatric genetics studies the constitution of the “control” or “normal” group has been based only on the absence of an overt expression of symptoms, where no particular emphasis is given to the symptom evaluation to exclude the phenotype.The use of psychometric instruments can help to assess some behavioral traits of clinical relevance. In turn, these assessments could help in the diagnosis, prognosis and treatment of disorders. Moreover, quantitative assessments let determine if these traits belong to the normal range of variation in a population or could be a deviation of the trend.
The Symptom Checklist 90 (SCL90) is a 90-item self-report inventory that assesses the level of distress recently experienced by the subject. It is comprised of nine dimensions: somatization, obsessive-compulsive, interpersonal sensitivity, depression, anxiety, hostility, phobic anxiety, paranoid ideation, psychoticism and a General Severity Index (GSI).
Although the SCL 90 is a well-accepted and widely used instrument in research and clinical practice in many countries, we found a scarcity of relevant studies for Latin America and a lack of normative data for Mexican populations. The aim of the present report was to evaluate the reliability and construct validity of the SCL 90.
Method
Subjects
A Spanish translation of the original SCL90 English version was administered to a group of 228 subjects, comprised by relatives of patients, members of a family parents association, medical and paramedical staff, and college students. The SCL90 was included within a battery of clinical and psychometric assessments of individuals participating at ongoing research protocols on the genetics of personality and creativity. An additional group of 30 ambulatory psychiatric patients from the Instituto Nacional de Psiquiatría Ramón de la Fuente (INPRF) was also analyzed. The instrument was applied by experienced qualified personal.
Statistical analyses Statistical analyses were performed using SYSTAT 8.0. Reliability was evaluated by assessing the response consistency obtained from those items with similar questions. The Cronbach’s alpha coefficient was used as the measure of the internal consistency for all nine subscales for this purpose. Construct validity was assessed using two complementary criteria: a) evaluating pre-conceptual hypotheses and b) analysing psychometric data. In the first case, and based on previous reports showing that the level of distress is a function of social-demographic, gender and clinical status, it was hypothesized that the mean scores should be higher in women, younger people and individuals affected with a psychiatric condition. ANOVA and F statistics were computed using the mean scores and standard deviations for the nine dimensions and GSI. In addition, the extent of correlation between individual items and its own subscale dimension should be higher than the other subscales, and the level of correlation between each item and the GSI should be positive. In this case, a Spearman rank correlation matrix was constructed for the SCL90 items and the nine subscales, as well as the GSI.
Results
Internal consistency
All but two of the nine SCL90 dimensions showed good internal consistency values (Cronmbach’s alphas ›0.7-0.85); with only hostility and paranoid ideation subscales reaching an acceptable value (›0.6-‹0.7). The overall Cronbach’s alpha score obtained for the GSI was 0.96.
Construct validity
Fifty-six of the SCL90 items showed a Spearman rank correlation coefficient value (r › 0.5), 23 items showed a moderate value (r ≥0.25 and ≤0.5), and only one item showed a weak correlation with its own scale (r =0.2). Only in one case (item 80) the highest correlation value did not correspond with its particular dimension.
Mean scores for all of the nine dimensions of the SCL90, as well as the GSI, were higher in women compared to men, and in subjects ‹ 25 years old. The ANOVA showed statistically significant differences (p‹ 0.01) for somatization, depression, obsessive-compulsive, interpersonal sensitivity, anxiety, hostility dimensions as well as for the GSI. Likewise, an ANCOVA, using age as a covariable, showed an age effect for the last five dimensions (p ‹ 0.005), and in lesser degree for paranoid ideation (p =0.014). Likewise, both men and women patients populations showed higher scores for each dimension compared to general population.
Comparison between Mexican and Argentine populations
Independent sample t test showed meaningful differences for three scales (obsessive compulsive, interpersonal sensitivity, anxiety, as well as for the GSI) in men and women. Somatization was statistically different only for women from Argentina.
Percentiles calculated for each one of all dimensions and the GSI showed a general tendency to be higher for the Mexican population compared with data from Argentina.
Discussion
The SCL90 is a self-report inventory where the subject reflects his/her perception about the degree of distress that he/she is experiencing. It is used by clinicians and researchers to gather information about the mental health of subjects. In the mental health field, the SCL90 has been employed world-wide to monitor the quality of the medical-psychological interventions, as well as a screening tool to identify psychopathology symptoms. We examined certain psychometric properties of the Spanish version of the SCL90, as there is a lack of normative data for Mexico. The internal consistency reliability for the scale as a whole and for individuals subscales was in general terms adequate for the group of individuals examined. Validity was assured throughout the confirmation of expected differences of groups of comparison and by the good correlation agreement among specific items and their particular dimensions. Compared to the only Latin American study, the mean scores for Mexican population were higher than in Argentina and even higher compared with the USA normative sample. Among others putative factors, translation issues (e.g. use of double negative sentences) and /or cross-cultural differences (e.g. demographic characteristics, socioeconomic differences) should be taken into account to explain these differences; therefore caution should be applied when comparing data of different populations.
Among the limitations of this study we must include the analysis of a non-population sample of modest size. Nonetheless, we can conclude that the SCL90 inventory shows good psychometric attributes that may be useful for research and/or clinical purposes. Percentiles rank data can be used as a starting reference for others researchers interested in evaluating in a fast and simple way the psychological distress status of a particular individual, underlying the necessity of developing on a short-term basis normative data for the Mexican population.
REFERENCES