Background: Quality of life (QoL) is a crucial outcome measure in patients with lower limb ischemia (LLI). The Short Form 36 (SF36) has been proposed as the gold standard instrument for generic QoL analysis in patients with LLI. The Short Form 8 (SF8) was developed from the SF36 and we aim to compare these two instruments in terms of validity, reliability, and responsiveness.
Methods: One hundred ninety-three patients, 135 men and 58 women, median age 66 (range, 44-84) years with LLI completed the SF36 and the SF8. Disease severity was graded according to International Society of Cardiovascular Surgery (ISCVS) suggested reporting standards. Correlation between the two instruments' like domains and non-like domains reflects convergent and divergent validity respectively. A subgroup of 58 patients (44 men) completed two sets of questionnaires, with an intervening period of 2 weeks. Correlation between these two sets of questionnaires was used to analyze test/retest reliability. Spearman's rank correlation was used to analyze validity and reliability. Responsiveness of the individual domains across the whole group was analyzed using the Kruskall-Wallis analysis of variance (ANOVA) test, while responsiveness between the groups of patients with varying severity of LLI was analyzed using the Mann-Whitney U test.
Results: There was greater correlation between like domains of SF36 and the SF8 than the non-like domains suggesting good convergent-divergent validity. Test/retest reliability was significant for both instruments (r(s) > 0.7). Increasing LLI resulted in a statistically significant deterioration in all eight domains of both instruments. The time taken was significantly shorter and less assistance was required to complete the SF8 than the SF36.
Conclusion: The SF8 is a valid and reliable QoL instrument in patients with LLI, and as it is simpler and quicker to complete, we suggest it may challenge the SF36 as the gold standard generic QoL analysis instrument in LLI.