A randomised comparison of a four- and a five-point scale version of the Norwegian Function Assessment Scale.
BACKGROUND
There is variation in the number of response alternatives used within health-related questionnaires. This study compared a four-and a five-point scale version of the Norwegian Function Assessment Scale (NFAS) by evaluating data quality, internal consistency and validity.


METHODS
All inhabitants in seven birth cohorts in the Ullensaker municipality of Norway were approached by means of a postal questionnaire. The NFAS was included as part of The Ullensaker Study 2004. The instrument comprises 39 items derived from the activities/participation component in the International Classification for Functioning, Disabilities and Health (ICF). The sample was computer-randomised to either the four-point or the five-point scale version.


RESULTS
Both versions of the NFAS had acceptable response rates and good data quality and internal consistency. The five-point scale version had better data quality in terms of missing data, end effects at the item and scale level, as well as higher levels of internal consistency. Construct validity was acceptable for both versions, demonstrated by correlations with instruments assessing similar aspects of health and comparisons with groups of individuals known to differ in their functioning according to existing evidence.


CONCLUSIONS
Data quality, internal consistency and discriminative validity suggest that the five-point scale version should be used in future applications.
Østerås
Nina
N
Section of Occupational Health and Social Insurance Medicine, Institute of General Practice and Community Health, Faculty of Medicine, University of Oslo, Norway. nina.osteras@medisin.uio.no
Gulbrandsen
Pål
P
Garratt
Andrew
A
Benth
Jūratë Saltytë
JS
Dahl
Fredrik A
FA
Natvig
Bård
B
Brage
Søren
S
D000203:Activities of Daily Living / Q000145:classification*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D004185:Disability Evaluation; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway; D015203:Reproducibility of Results; D018582:Sick Leave; D011795:Surveys and Questionnaires