Background/Purpose:

Economic evaluation of health care activities requires often measuring clinical symptoms and their changes also in monetary terms. Patients with rheumatoid arthritis (RA) may experience morning stiffness (MS), which varies over time, reflecting both short-term fluctuation in symptoms and long-term disease progression. A method that has been successfully applied to measure symptoms of RA is contingent valuation, and particularly its form called Willingness-To-Pay approach (WTP). In this method, patients are asked the maximum amount they would be willing to pay in order to reach a certain health status. In earlier studies patients with more severe symptoms have been willing to pay higher amounts than those with less symptoms. However, it is not known whether the fluctuation in symptoms is reflected in the amounts produced by WTP method. In order to serve as a useful method for monetary valuation of symptoms, WTP approach should produce values which reflect also the changes in symptoms.

The aim of this study was to determine the within-patient variation in duration of MS over 1 year, and the corresponding monetary equivalents assigned to its changes using WTP methodology.

Methods:

The sample (n=100) comprised patients with RA from Turku University Hospital, Finland. All patients were interviewed twice by a trained interviewer using the same interview, 1 year apart. Patients estimated duration of MS in minutes. They were also asked to estimate how much they would be willing to pay on a daily basis if MS could be reduced by 25%, 50%, 75% and 100%. Weighted average of the monetary assessment for MS reduction was computed. Statistical evaluation was based on paired samples t-test, one way analysis of variance and linear regression model.

Results: After 1 year, there was a highly significant reduction in average MS duration from 44.7 minutes to 41.4 minutes (p<0.001); duration was reduced in 34.7% of patients, unchanged in 34.7% and prolonged in 30.6%. Weighted group average WTP for MS duration reduction was € 13.75 in the first interview and € 14.26 a year later (p<0.001). Changes in MS duration were reflected in within-patient WTP estimates. Among patients with reduced MS, weighted average WTP was reduced by € 18.46, in patients with unchanged duration, weighted average WTP increased by € 4.89, and in patients with increased duration of MS, weighted average WTP increased by € 13.46 (p<0.05). This pattern was statistically significant (p<0.05) for hypothetical reduction in MS duration of 50%, 75% and 100%, but not for 25% reduction in MS duration. Changes in duration of MS explained significantly (p<0.05) the variation in change of WTP for reduction, also when level of income was simultaneously controlled (R²=0.325).

Conclusion:

Duration of MS varied considerably over the 1 year follow-up. WTP estimates and their changes corresponded closely to changes in MS duration. WTP method can be considered a valid method to evaluate the impact of morning stiffness in patients in monetary terms.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/measuring-economic-value-of-morning-stiffness-consistency-over-1-year/