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Establishing construct validity for the thyroid-specific patient reported outcome measure (ThyPRO): an initial examination

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Abstract

Objective

To establish a reliable and valid scale structure of a patient-reported outcome measuring thyroid-specific quality of life.

Methods

The 98-item ThyPRO questionnaire was administered to patients with benign thyroid diseases at two university hospitals. Multi-trait scaling was performed, evaluating lack of convergent validity (item-own scale polyserial correlation <0.40) or lack of discriminant validity (item-other scale correlation higher than item-own scale correlation) of the hypothesized scale structure. Analyses were repeated in clinical and sociodemographic subgroups and with Pearson correlations. Reliability was estimated by Cronbach’s α, both conventionally and with polychoric correlations.

Results

In total, 904 patients (69%) responded. Initial multitrait scaling analysis identified 25 scaling errors. Twelve items were omitted from the scale structure, and a re-analysis showed complete convergent validity and only two instances of lack of discriminant validity. Pearson correlations yielded similar results. Across all subgroups, convergent validity was complete, and discriminant validity was found in 99.2% of tests. Lack of discriminant validity was mainly between physical symptoms and psychological and disease-impact scales. Cronbach’s α was acceptable (>0.70, >0.80 with polychoric correlations) for all 13 scales.

Conclusion

A reliable scale structure displaying complete convergent and almost complete discriminant validity was established in general analyses and in distinct clinical subgroups of patients with benign thyroid diseases.

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Acknowledgements

We wish to express our gratitude to the staffs and colleagues at Rigshospitalet Endocrinological Department PE 2131 and 5201 and Odense University Hospital, Department of Endocrinology and Metabolism. Special thanks go to our research assistants Sara Hope Watt and Alexandra Hegedüs. This study has been supported by grants from the Danish Medical Research Council, Agnes and Knut Mørk’s Foundation, Aase and Ejnar Danielsen’s Foundation, Else and Mogens Wedell-Wedellsborg’s Foundation, the Genzyme Corporation, the Novo Nordisk Foundation and the Danish Thyroid Foundation.

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Authors and Affiliations

  1. Department of Endocrinology, Copenhagen University Hospital Rigshospitalet, Blegdamsvej 9, 2100, Copenhagen Ø, Denmark

    Torquil Watt, Åse Krogh Rasmussen & Ulla Feldt-Rasmussen

  2. Institute of Public Health, University of Copenhagen, Copenhagen, Denmark

    Torquil Watt, Jakob Bue Bjorner & Mogens Groenvold

  3. National Research Centre for the Working Environment, Copenhagen, Denmark

    Jakob Bue Bjorner

  4. Department of Palliative Medicine, Bispebjerg Hospital, Odense University Hospital, Odense, Denmark

    Mogens Groenvold

  5. Department of Endocrinology and Metabolism, Odense University Hospital, Odense, Denmark

    Steen Joop Bonnema & Laszlo Hegedüs

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  1. Torquil Watt
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Correspondence to Torquil Watt.

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Researchers who want to use the ThyPRO may contact the first author (T.Watt@rh.dk).

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Watt, T., Bjorner, J.B., Groenvold, M. et al. Establishing construct validity for the thyroid-specific patient reported outcome measure (ThyPRO): an initial examination. Qual Life Res 18, 483–496 (2009). https://doi.org/10.1007/s11136-009-9460-8

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