Background: The present study, performed within the International Quality of Life Assessment project (including researchers from 15 countries) presents preliminary results of the process of adaptation of the SF-36 to be used in Spain.
Methods: The adaptation was based on the translation/back-translation methodology. Meetings of translators, researchers and patients were organized in order to produce successive versions. A study involving 47 individuals was carried out to assess the relative value (through a visual analogue scale) of each response choice of the questionnaire items. Finally, internal consistency and reproducibility of the Spanish version of the SF-36 was assessed by administering the questionnaire to 46 patients with stable coronary heart disease in two different occasions 2 weeks apart.
Results: The average ratings of equivalence of the translated version with the original were high regardless of the difficulty of translation. The rank ordering of mean scores for each responses choice agreed with the ranking assigned in the questionnaire in all cases. Cronbach's Alpha was higher than 0.7 for all dimensions (range: 0.71-0.94) except for Social Functioning scale (alpha = 0.45). Intraclass correlation coefficients between both administrations of the questionnaire ranged from 0.58 to 0.99.
Conclusions: The adaptation process of the SF-36 has concluded with an instrument apparently equivalent to the original and with an acceptable level of reliability. Nevertheless, other basic characteristics of the adapted questionnaire (i.e. validity and sensitivity to changes) should be also assessed.