Xuxi Zhang

DISCUSSION In the present study, within a diverse community ‐ based sample of older people in Spain, Greece, Croatia, the Netherlands and the UK, we found an internal consistency of the full TFI and the physical domain in the total population and in each country. However, the internal consistency of the psychological and social domains was not satisfactory. Our results further support the convergent and divergent validity of the 3 domains in the total population and in each country. The concurrent validity of the full TFI and the 3 domains were supported in the total population and in each country, except for the social domain in Croatia. Regarding the full TFI, the reliability was satisfactory with an internal consistency of the Cronbach alpha  ≥ 0.70 in the total population and in each country. Previous studies in the Netherlands, 12 Portugal, 16 Poland, 18 Brazil, 15 and China 22 found similar results. The concurrent validity was acceptable with most AUCs  ≥ 0.70 in the total population and in each country. This finding was similar to previous studies on the full TFI in the Netherlands, 12 Italy, 38 and China 22 . Regarding the physical domain, the internal consistency was satisfactory in the total population and in Croatia and the Netherlands, which was consistent with previous studies. 12, 15, 16, 18, 22 The Cronbach alpha of the physical domain in Spain, Greece and the UK varied between 0.60 and 0.67. Earlier studies in Germany, 17 Italy, 38 and Spain 19 reported similar results and concluded that the internal consistency was acceptable with the Cronbach alpha ≥ 0.60. The convergent and divergent validity was supported in the total population and in each country, which was consistent with previous studies. 12, 17, 22, 38 The concurrent validity was acceptable in the total population and in each country, which was consistent with previous studies on the physical domain in the Netherlands, 12 Italy, 38 and China 22 . Regarding the psychological and social domains, the internal consistency was satisfactory in none of the countries with the Cronbach alpha varying between 0.22 and 0.55. Previous studies reported similar findings. 12, 15, 16, 18, 22 The low internal consistency for the psychological and social domains might be caused by their small number of items. 12, 15 The Cronbach alpha increases with number of items. Therefore, adding items to the psychological and social domains would be beneficial, for instance items referring to feelings of insecurity and the number of social contacts. 5 In addition, the low Cronbach alpha values do not imply that the items of the psychological and (especially) social domains are invalid, but rather they function more as an index rather than as a scale. The convergent and divergent validity was supported in the total population and in each country. The concurrent validity of the psychological domain was acceptable in the total population and in each country and that of the social domain acceptable in all countries except Croatia. We recommend further studies on the social domain in Croatia, for instance, cultural adaptation of the items in the social domain. A previous study in China also reported an acceptable concurrent validity of the 92 Chapter 4