The sickness impact profile: SIP68, a short generic version. First evaluation of the reliability and reproducibility

In previous research a short version of the Sickness Impact Profile (SIP136) was developed, containing 68 items. This SIP68 is intended as a short generic alternative to the original SIP. High reliability of the SIP68 was reported when it was extracted from the SIP136. This paper is a report on the first reliability testing of the SIP68 administered as an independent instrument without the context of the SIP136. To establish the test-retest reliability and the internal consistency of the new instrument, 51 patients of an outpatient department of rheumatology completed the SIP68 twice, with an interval of 48 hours. To compare the performance of the independent SIP68 with the SIP68 extracted from the SIP136, the SIP136 also was completed two times by the same 51 respondents. Test-retest reliability for both administration types was assessed by means of the intraclass correlation coefficient and the Jaccard's similarity ratio. Internal consistency was assessed by means of Cronbach's alpha. The reliability appears to be high in both the independent SIP68 as well as the extracted SIP68. Moreover, the reliability of the independent SIP68 appears to be as high as for the SIP136. These findings were very encouraging, indicating that the SIP68 may very well serve as a generic alternative to the SIP136.