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Open Access Research article

Factorial validity and internal consistency of the PRAFAB questionnaire in women with stress urinary incontinence

Erik JM Hendriks123*, Arnold TM Bernards12, J Bart Staal13, Henrica CW de Vet4 and Rob A de Bie13

Author Affiliations

1 Department of Epidemiology and Centre for Evidence Based Physiotherapy & Clinical Guidelines (CEBP), Maastricht University, Maastricht, The Netherlands

2 Department of Research and Development, Dutch Institute for Allied Health Care (NPi), Amersfoort, The Netherlands

3 Caphri Research Institute, Maastricht University, The Netherlands

4 EMGO Institute, VU University Medical Center, Amsterdam, The Netherlands

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BMC Urology 2008, 8:1  doi:10.1186/1471-2490-8-1

Published: 24 January 2008

Abstract

Background

To investigate the factor structure, dimensionality and construct validity of the (5-item) PRAFAB questionnaire score in women with stress urinary incontinence (stress UI).

Methods

A cross validation study design was used in a cohort of 279 patients who were randomly divided into Sample A or B. Sample A was used for preliminary exploratory factor analyses with promax rotation. Sample B provided an independent sample for confirming the premeditated and proposed factor structure and item retention. Internal consistency, item-total and subscale correlations were determined to assess the dimensionality. Construct validity was assessed by comparing factor-based scale means by clinical characteristics based on known relationships.

Results

Factor analyses resulted in a two-factor structure or subscales: items related to 'leakage severity' (protection, amount and frequency) and items related to its 'perceived symptom impact' or consequences of stress UI on the patient's life (adjustment and body (or self) image). The patterns of the factor loadings were fairly identical for both study samples. The two constructed subscales demonstrated adequate internal consistency with Cronbach's alphas in a range of 0.78 and 0.84 respectively. Scale scores differed by clinical characteristics according to the expectations and supported the construct validity of the scales.

Conclusion

The findings suggest a two-factorial structure of the PRAFAB questionnaire. Furthermore the results confirmed the internal consistency and construct validity as demonstrated in our previous study. The best description of the factorial structure of the PRAFAB questionnaire was given by a two-factor solution, measuring the stress UI leakage severity items and the perceived symptom impact items. Future research will be necessary to replicate these findings in different settings, type of UI and non-white women and men.