The Finnish version of FAST showed similar excellent psychometric properties as the original version regarding internal consistency and test-retest reliability. Furthermore, the correlation with well-known previous scales assessing functioning, namely the SOFAS and the SDS, was high.
In addition to Spanish and English, the FAST has been translated into Italian (Moro et al. 2012, Barbato et al. 2013), Portuguese (Cacilhas et al. 2009), and Turkish (Aydemir and Uykur 2012) and now also Finnish. The psychometric properties of the Finnish version of FAST showed high internal consistency, in accord with earlier studies. Furthermore, the reliability of the scale, as evaluated by two different clinicians blind to each other’s findings, was excellent (correlation coefficient 0.896). FAST includes the following six areas of functioning: autonomy, occupational functioning, cognitive functioning, financial issues, interpersonal relationships, and leisure time. The reliability for domains regarding autonomy, occupational functioning, and cognitive functioning was excellent, whereas for domains regarding financial issues, interpersonal relationships, and leisure time, the reliability was good. These domains are potentially more difficult to assess over a short period. We also compared FAST with the commonly used and well-known scales of SOFAS and SDS. The correlations between FAST and SOFAS and between FAST and SDS were good. In addition, the correlation between FAST occupational functioning and SDS work domain was good. Finally, we investigated the validity of FAST according to employment status and experienced work ability. The scores of employed subjects were significantly lower than the scores of subjects with sick leave or disability pension. Also, subjective ability to work correlated well with FAST scores. Thus, the results confirm previous findings that higher scores in FAST are associated with poorer functioning.
This study has some limitations. We did not have healthy controls to analyse the scale’s capacity to discriminate between patients and controls. However, previous studies have examined this and have reported the optimal cutoff on the FAST total score for discriminating patients from controls to be 11 (Rosa et al. 2007, Moro et al. 2012) or 15 (Barbato et al. 2013). The sample size of the study was also modest. However, our results were statistically highly significant and similar to those of earlier studies. Furthermore, we did not investigate sensitivity to change, which is a critical feature of a scale in outcome studies, and it should be investigated in the future. However, in other studies, the original FAST has demonstrated sufficient sensitivity to change (Rosa et al. 2011; Torrent et al. 2013). Finally, the translation was conducted by the clinical research group in collaboration with researchers of the Barcelona Bipolar Disorders program. Issues of cross-cultural adaptation (see Epstein et al. 2015) were explicitly discussed between the two groups, and back-translation was undertaken, but no focus group or expert committee was available.