Date Published: April 5, 2019
Publisher: Public Library of Science
Author(s): Katja Petrowski, Bjarne Schmalbach, Sören Kliem, Andreas Hinz, Elmar Brähler, Iratxe Puebla.
The SCL-K-9 is the latest short version of the multidimensional Symptom-Checklist 90-R. Up to now, its psychometric properties have not been clarified sufficiently as the nine items have not yet been presented exclusively in a representative sample. Therefore, psychometric properties, model fit values as well as norm-values were analyzed.
For the sample, N = 2,507 participants aged 14 to 92, n = 1,379 women and n = 1,128 men, and a mean age of 48.79 (SD = 17.91), were selected from the general population by random-route sampling. Confirmatory factor analyses applying full information maximum likelihood (FIML) tested the model fit. The reliability estimations and effect sizes were reported.
The items’ discriminative power ranged between .49 to .65, and the Cronbach’s Alpha was α = .87, which stands for a good reliability of the SCL-K-9. Norm values as well as gender and age specificities were presented in this section. The CFA with all nine items loading on one latent factor resulted in a good fit. There was evidence of invariance across age and gender groups.
Based on these results, the short screening version SCL-K-9 of the Symptom-Checklist 90-R showed good reliability and good model fit; specific norm values could be determined. Further studies should evaluate the usefulness of the standardization in clinical samples.
The Symptom-Checklist SCL-90-Revised [1, 2] and its short forms are the multidimensional screening instruments for mental symptoms in psychotherapy research employed most frequently [3, 4, 5]. The instrument includes subscales for depressive, dysthymic, vegetative, agoraphobic, and socio-phobic symptoms as well as symptoms of distrust and a general severity index (GSI). The GSI is considered the best indicator for global psychological distress . Several representative samples with over 4, 500 individuals filled out the Symptom-Checklist SCL-90-Revised . Satisfactory reliability and an almost identical six- factorial structure could be shown consistently . However, statistical test shortcomings in the SCL-90-R were observed in patients with chronic pain [8, 9]. In addition, the allocation of the items to the nine scales was suboptimal in psychiatric patients as well as in healthy individuals [10, 11, 12]. As statistical shortcomings in the SCL-90-R had been observed, several short versions were developed, each with a different number of items [8, 9].
The SCL-90  is the questionnaire most frequently used internationally to assess psychological distress, especially in clinical practice [47, 48, 49, 50], but it is a very extensive and time-consuming questionnaire. Therefore, short versions were developed for use in large representative studies. One of these is the SCL-K-9 version. The psychometric properties of this version were analyzed in the present study. Internal consistency measured with Cronbach’s Alpha was .87, which stands for a good reliability of the SCL-K-9. Hereby, a low value of alpha could be due to, first of all, a low number of questions, second, a poor interrelatedness between items or, third, a heterogeneous construct. Furthermore, a too high Cronbach’s Alpha value may suggest that some of the items are redundant as the questions refer the same matter but are phrased differently (i.e. item wording). Since in this context a maximum alpha value of 0.90 has been recommended , the value determined here may be judged as positive.