Susi Ari Kristina, Dwi Endarti, Tri Murti Andayani, M. Rifqi Rokhman


Objective: To estimate validity and reliability of WTP questionnaire which WTP value can be taken as an indication of the monetary value of health gains, which may carry information regarding the appropriate height of the cost-effectiveness threshold.

Methods: Three hundred respondents, in Yogyakarta province, Indonesia, were interviewed during June 2017. We examine a value of WTP associated with the following scenarios: 1) improving moderate condition; 2) extending life during terminal illness, and 3) lifesaving. The interview ascertained maximum hypothetical WTP for one QALY using a dichotomous bidding format with an open-ended final question, along with questions about the socio-economic factors. Concerning validity, the WTP of the 3 versions of hypothetical scenarios were compared as known-group validity and analysis of the sensitivity and specificity was performed. Test-retest reliability and alpha Cronbach were employed to measure internal consistency.

Results: Analysis generally confirmed the validity and reliability of the WTP hypothetical scenarios. In terms of known group validity, there was significant difference across two scenarios (treatment v. s lifesaving), but no significant difference between mean WTP for treatment and terminal illness was found. Mean WTP for terminal illness (38 Million IDR) and lifesaving scenario (16 Million IDR) was significantly higher than that of treatment scenario (14 Million IDR). The WTP instrument showed good convergent validity (r=0.784), when comparing correlation between WTP value and utility score. Estimation of scenario’s sensitivity and specificity in deriving expected WTP were 70.33 % and 38.98 %, respectively. The positive and negative predictive values were 64 % and 46 %. The test-retest reliability of WTP values indices excellent stability and reliability of the instrument with Spearman’s rank correlation coefficient of 0.816 (p<0.001)

Conclusion: This study demonstrated that the WTP instrument is feasible and relatively reliable for measuring the WTP values in Indonesia. For wider application of the instrument, its validity should be investigated further. Meanwhile, adoption of WTP as an empirical evidence of societal values is encouraged. 


Reliability, validity, hypothetical scenario, Willingness-to-pay

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Thavorncharoensap M, Teerawattananon Y, Natanant S, Kulpeng W, Yothasamut J, Werayingyong P. Estimating the willingness to pay for a quality-adjusted life year in Thailand: does the context of health gain matter? Clinicoecon Outcomes Res 2013;5:29-36.

Nimdet K, Chaiyakunapruk N, Vichansavakul K, Ngorsuraches S. A systematic review of studies eliciting willingness-to-pay per quality-adjusted life year: does it justify CE threshold? PLoS One 2015;10:e0122760.

Shillcutt SD, Walker DG, Goodman CA, Mills AJ. Cost effectiveness in low-and middle-income countries: a review of the debates surrounding decision rules. Pharmacoeconomics 2009;27:903-17.

Kristina SA, Endarti D, Prabandari YS, Ahsan A, Thavorncharoensap M. Burden of cancers related to smoking among the indonesian population: premature mortality costs and years of potential life lost. Asian Pac J Cancer Prev 2015;16:6903-8.

Pinto-Prades JL, Loomes G, Brey R. Trying to estimate a monetary value for the ALY. J Health Econ 2009;28:553-62.

Mason H, Baker R, Donaldson C. Willingness to pay for a QALY: past, present and future. Expert Rev Pharmacoecon Outcomes Res 2008;8:575-682.

Olsen JA, Smith RD. Theory versus practice: a review of 'willingness-to-pay' in health and health care. Health Econ 2001;10:39-52.

Bobinac A, Van Exel NJ, Rutten FF, Brouwer WB. Willingness to pay for a quality-adjusted lifeyear: the individual perspective. Value Health 2010;13:1046-55.

Zhao FL, Yue M, Yang H, Wang T, Wu JH, Li SC. Willingness to pay per quality adjusted lifeyear: Is one threshold applicable for all decision-making? Value Health 2010 13:A538.

Shiroiwa T, Sung YK, Fukuda T, Lang HC, Bae SC, Tsutani K. International survey on willingness-to-pay (WTP) for one additional QALY gained: what is the threshold of cost effectiveness? Health Econ 2010;19:422-37.

Lieu TA, Ray GT, Ortega-Sanchez IR ea. Willingness to pay for a QALY based on community member and patient preferences for temporary health states associated with herpes zoster. Pharmacol Economics 2009;27:1005-16.

Wagner TH, Wu T, Duenas GV, Pasick RJ. Willingness to pay for mammography: item development and testing among five ethnic groups. Health Policy 2000;53:105-21.

Weinstein MC. How much are Americans willing to pay for a quality-adjusted life year? Med Care 2008;46:343-5.

Bhatia MR, Fox-Rushby JA. Validity of willingness to pay: hypothetical versus actual payment. Appl Economics Lett 2003;10:737-40.

Cook DA, Beckman TJ. Current concepts in validity and reliability for psychometric instruments: theory and application. Am J Med 2006;119:166, e7- e16.

Smith RD, Richardson J. Can we estimate the “social” value of a QALY? Four core issues to resolve. Health Policy 2005;74:77-84.

Gyrd-Hansen D, Kjaer T. Disentangling WTP per QALY data: different analytical approaches, different answers. Health Econ 2012;21:222-37.

Shiroiwa T, Igarashi A, Fukuda T, Ikeda S. WTP for a QALY and health states: More money for severer health states? Cost Effectiveness Resource Allocation 2013;11:22.

Krabe PFM, Essink-Bot ML, Bonsel GJ. The comparability and reliability of five health-state valuation methods. Soc Sci Med 1997;45:1641-52.

Mahmudah RL, Ikawati Z, Wahyono D. A qualitative study of perspective, expectations, and needs of education in chronic obstructive pulmonary disease (COPD). Int J Chem Pharm Res 2017;9:32-5.

Park H. Association between rheumatoid arthritis and health-related quality of life in Korean women aged 50 y and over. Asian J Pharm Clin Res 2017;10:372-5.

Pinto-Prades JL, Sanchez-Martinez FI, Corbacho B, Baker R. Valuing QALYs at the end of life. Soc Sci Med 2014;113:5-14.

Martin-Fernandez J, Polentinos-castro E, del Cura-Gonzalez MI, Ariza-Cardiel G, Abraira V G-PS. Willingness to pay for a quality-adjusted life year: an evaluation of attitudes towards risk and preferences. BMC Health Serv Res 2014;14:28.

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Reliability, validity, hypothetical scenario, Willingness-to-pay





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International Journal of Pharmacy and Pharmaceutical Sciences
Vol 9, Issue 12, 2017 Page: 288-292

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Authors & Affiliations

Susi Ari Kristina
Department of Pharmaceutics, Faculty of Pharmacy, Universitas Gadjah Mada, Yogyakarta, Indonesia

Dwi Endarti
Department of Pharmaceutics, Faculty of Pharmacy, Universitas Gadjah Mada, Yogyakarta, Indonesia

Tri Murti Andayani
Department of Pharmacology and Clinical Pharmacy, Faculty of Pharmacy, Universitas Gadjah Mada, Yogyakarta, Indonesia

M. Rifqi Rokhman
Department of Pharmaceutics, Faculty of Pharmacy, Universitas Gadjah Mada, Yogyakarta, Indonesia

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