In general , estimates of construct validity were lower when vali date d against dissimilar constructs , except for instruments measuring impairments in mental functions .
CONCLUSION There is a trend that validation against a similar construct yields higher correlation coefficients than validation against a dissimilar construct .
PURPOSE This paper focuses on the construct validity of instruments measuring impairments in body structures and function in rheumatic disorders .
The objective is : 1 ) to make an inventory of constructs , based on the domains of the International Classification of Functioning , Disabilities and Health problems ( ICF ) , against which instruments measuring impairments in body structures and function were vali date d ; 2 ) to analyse whether validation against a similar construct result ed in higher correlation coefficients than validation against a dissimilar construct .
Defining disease activity in ankylosing spondylitis: is a combination of variables (Bath Ankylosing Spondylitis Disease Activity Index) an appropriate instrument?
OBJECTIVE Disease activity has been defined using a self-administered instrument , focusing on fatigue , axial pain , peripheral pain , enthesopathy and morning stiffness [ Bath Ankylosing Spondylitis Disease Activity Index ( BASDAI ) ] . This vali date d instrument is simple and takes 40 s to complete , but whether the index is an accurate expression of the component parts , or whether additional weighting would enhance its efficacy , is unclear . METHODS Four hundred and seventy-three patients with ankylosing spondylitis received placebo or active non-steroidal anti-inflammatory drug ( NSAID ) for 6 weeks , and changes between entry and completion were captured by BASDAI and the individual components . Principle component analysis ( PCA ) was used to explore the best combinations of variables in decreasing order of explained total dispersion and to assess whether a single sum ( or algebraic expression ) best defined disease activity status . RESULTS At entry , the correlation between BASDAI and the first axis was 0.99 , 0.11 with the second , and zero thereafter . Data at study end and relating to change revealed a 100 % correlation ( R = 1 ) between the first axis and the sum , with zero for the remainder . CONCLUSIONS The data support BASDAI as being a valid and appropriate composite to define disease activity in ankylosing spondylitis . Developed as a simple sum of its components , BASDAI has excellent content validity
In general , estimates of construct validity were lower when vali date d against dissimilar constructs , except for instruments measuring impairments in mental functions .
CONCLUSION There is a trend that validation against a similar construct yields higher correlation coefficients than validation against a dissimilar construct .
PURPOSE This paper focuses on the construct validity of instruments measuring impairments in body structures and function in rheumatic disorders .
The objective is : 1 ) to make an inventory of constructs , based on the domains of the International Classification of Functioning , Disabilities and Health problems ( ICF ) , against which instruments measuring impairments in body structures and function were vali date d ; 2 ) to analyse whether validation against a similar construct result ed in higher correlation coefficients than validation against a dissimilar construct .