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Abstract
The purpose was to introduce the Rasch model by showing an application in nursing
research.
The Rasch model was used to examine the psychometric properties of the nursing self-efficacy
(NSE) scale. Data were collected among nursing students in Sweden. Two sets of items
were analysed more thoroughly: an original set of nine items with eleven response
categories and a revised set of seven items with seven response categories. Invariance
of the item functioning and the categorisation of the items were analysed. Targeting
was examined by comparisons of the items and persons locations. Differential Item
Functioning across sample groups such as gender was examined using analysis of variance.
The final set of seven items was also analysed more closely with respect to possible
multidimensionality and response dependence.
The Rasch analysis of the original set of nine items showed high reliability measured
by a person separation index, but it also indicated severe problems with the targeting,
the categorisation of the items as well as lack of invariance. Although the revised
set comprising seven items with seven categories performed better than the original
item set some items showed misfit according to formal test statistics. Graphical examination
showed, however, that the items operated in the right direction. The formal test of
local independence of the items indicated minor signs of multidimensionality, alternatively
response dependence.
The Rasch model is useful for rigorous examination and development of measurement
instruments in nursing research. The Rasch model facilitates disclosure of lack of
invariance and other measurement problems that may not be easily detected by traditional
analyses. Hence, the NSE-scale would probably have performed much better if the developmental
work had been guided by Rasch analyses. In future work on the scale, priority should
be given to improving the targeting and the categorisation of the items.