The second instrument we administered was the Sickness Impact Profile (SIP).
Test-retest reliability (r=0.92) is high using various scoring methods.[5] The internal consistency of the SIP is Cronbach's alpha=0.94.17 The Sickness Impact Profile is valid when measured against other instruments: self assessment, physician rating, Katz ADL items from the National Health Interview Survey, and multiple physiologic measures.[6] A higher correlation with measures of physical dysfunction than with sickness is noted in this study, which is particularly useful for the population in this investigation.