Translation into Brazilian Portuguese, cross-cultural adaptation and validation of the Stanford presenteeism scale-6 and work instability scale for ankylosing spondylitis

Loss of productivity at work, as a result of health problems, is becoming an issue of interest due to the high burden it represents in society. The measurement of such phenomenon can be made using generic and specific scales for certain diseases such as the Stanford Presenteeism Scale (SPS-6) and the Work Instability Scale for Ankylosing Spondylitis (AS-WIS), specific for patients with ankylosing spondylitis (AS). The aim of this study was to translate and perform a cross-cultural adaptation of SPS-6 and AS-WIS into Portuguese and check their psychometric properties. The study also aimed to evaluate the relationship between the general scores of the scales and the main sociodemographic and clinical data, lifestyles, and absenteeism in patients with AS and correlate these variables with SPS-6 and AS-WIS scales. A sample of 120 patients with AS and 80 workers at a university hospital was evaluated. The processes for the translation and cross-cultural adaptation of the instruments followed preestablished steps and rules presented in the literature. For the evaluation of measurement properties and correlations between scales, intra-class correlation coefficient (reproducibility analysis), Cronbach alpha (internal consistency), and Pearson correlation coefficient (validity) were employed. The inter-observer (0.986) and intra-observer (0.992) reproducibilities of the AS-WIS were shown to be high as well as the internal consistency (0.995). Similarly, the inter-observer reliability of SPS-6 was considered good (0.890), although it showed a poorer performance when considering the same observer (Pearson correlation coefficient = 0.675 and intra-class correlation = 0.656). Internal consistency, for the total number of items, as measured by Cronbach alpha, was 0.889. The validity of the scales was evaluated thru the comparison of the achieved scores with the results of the WLQ, SF-36, ASQoL, BASFI, BASDAI, HAQ-S, and SRQ-20 instruments. Correlations between loss of productivity at work, worse quality of life, presence of emotional disturbances, and worse health conditions were positive. The process of translation, cross-cultural adaptation, and validation of the SPS-6 as a generic measurement for the loss of productivity at work and of the AS-WIS as a specific measurement for patients with AS are valid, reproducible, and specific instruments to be used in Brazil. In both scales, productivity at work was associated to advanced age, higher rate of absenteeism in the last month and year, presence of peripheral arthritis, and a larger number of comorbidities in patients with AS. The AS-WIS and SPS-6 showed a good correlation among them although they are not mutually exclusive but supplementary.