Due to constraints of health care resources, health resource allocation decisions will increasingly rely on the results of health economic studies in particular cost-effectiveness (CE) analysis.  However, the presentation of cost-effectiveness analysis’ results as cost per unit of health outcome e.g. Quality-Adjusted Life Year (QALY) is still arbitrary for policy makers to decide whether the technology is cost-effective. By using the concept of “ceiling threshold”, if the cost-effectiveness ratio of new health intervention is not greater than the “threshold”, then the health technology is deemed to be cost-effective and is appropriatethe support using public finance.  Presently, there is no scientific standard for ceiling threshold. Furthermore, all countries are different in term of various socio-economic factors hence specific CE threshold is required for each country.
	This study aims to assess the willingness to pay per quality-adjusted life year (WTP/QALY) for use as a CE threshold in determining the cost-effectiveness of health interventions in Thailand.  This study is a cross-sectional survey. In this study, 1,191 sample aged between 15-65 years old from 9 provinces throughout the country namely Bangkok, Auanthog, Chonburi, Chiangmai, Pa-yao, Khonkaen, Surin, Trung, and Chumporn were interviewed during March - May 2008. The questionnaire consisted of three main components, namely general information, utility measure, and willingness to pay. There were 3 versions of questionnaires. Version 1 focused on scenario about blindness while version 2 and 3 were centered on scenarios about paralysis and allergy. For each version, 2 levels of disease severity were specified as follows; version 1: unilateral blindness and bilateral blindness; version 2: paraplegia and quadriplegia, and version 3: mild allergy and moderate allergy. Utility of current health state and hypothetical health states was measured using TTO and VAS while willingness to pay was measured using bidding game technique. Each respondent was asked to determine his/her maximum willingness to pay for treatment and prevention situation. For treatment situation, 5-year period of illness followed by complete recovery is assumed. For prevention situation, willingness to pay (WTP) to eliminate 40% risk (from 50% to 10%) was asked. Then, WTP/QALY is determined by univariate analysis and multivariate analysis using Mixed model. 
	According to the univariate analysis result, WTP/QALY for treatment situations are all higher than WTP/QALY for prevention scenario in all three hypothetical health scenario. Median WTP/QALY thresholds for treatment ranged from 24,281 Baht           (treatment of moderate allergy) to 115, 577 Baht (treatment of unilateral blindness) On the other hand, median WTP/QALY thresholds for prevention situation ranged from 9,054 Baht (prevention of paraplegia) to 47, 563 Baht (prevention of unilateral blindness). When disease severity was taken into account, WTP/QALY for scenarios with low severity was higher than that of high severity in all three hypothetical health scenarios both for treatment and prevention. These findings indicate the exit of the ceiling effect. It could be explained by the fact that willingness to pay for treatment and prevention with higher disease severity was equal or only slightly higher than willingness to pay for treatment and prevention with lower severity disease due to the limitation of ability to pay. On the other hand, situation with higher disease severity seemed to have significantly higher negative effect on quality of life, as compared to situations with lower of severity. 
	The results from multivariate analysis found that after controlling for other factors i.e. (gender, household income, hypothetical health scenario, and location of resident), WTP/QALY for treatment was estimated at 105, 669 Baht or approximately 1 time of Gross Domestic Product per capita in 2008 in Thailand. Similar to the findings from univariate analysis, WTP/QALY for treatment situation was higher than WTP/QALY for prevention scenario. In this case, WTP/QALY for prevention scenario was estimated at 53,382 Baht or approximately 0.5 time of Gross Domestic Product per capita in 2008. These findings seemed to be consistent with the thresholds derived from the thresholds currenty used in several countries e.g. the United States, Canada, Australia, and New Zealand. According to the review, the threshold used for resource allocation in those countries was approximately 1 – 2 times of Gross Domestic Product per capita in 2008. In addition, the threshold of 3 times of GDP per capita recommended by the Commission on Macroeconomics and Health[1]  seemed to be higher, as compared to the current threshold used in those countries. In Thailand, these findings also appeared to be consistent with the threshold set by the subcommittee for Development of the National List of Essential Drug (lower bound = 1 time GDP per capita / QALY, upper bound = 3 time GDP per capita / QALY). [2] On the other hand, the threshold for prevention situation found in this study was relatively low, as compared to the current threshold.   The findings also pointed out that the samples might perceive that unit cost of prevention should be less than unit cost of treatment or they might perceive prevention as less important than treatment. In the later case, policy makers and other stakeholders should pay more attention in providing knowledge, and employing effective strategy for attitude changing to increase the awareness of the importance of prevention intevention. 
This is a preliminary study with some limitations. A bigger study addresses thses questions should also be conducted to ensure representativeness of the samples. Also, the future study should employ more rigorous method that could control the ceiling effect, and represented various hypothetical health scenarios.  Furthermore, WTP/QALY should be calculated in term of function of several factors such as context, age, and gender, not just only a single value. 
Finally, any value of ceiling threshold should be perceived as one of the criteria in resource allocation. When making real policy decisions, other factors such as ethic, short and long-term budget impact, and availability of alternatives should also be taken into account. By using only CE as a sole criterion for resource allocation might lead to problems of unaffordability or uncontrolled growth in health care expenditure.In addition, it might cause ethical problems or lead to inappropriate health policy.