Table 2. Estimates of total incremental costs and effects due to SBI intervention and their 95% confidence interval (between brackets). Life years gaineda (*1,000) QALYs gaineda (*1,000) Costs SBI (* J1,000,000)b Total costs differences (* J1,000,000)b J per life year gainedc* J per QALY gainedc* J per life year gainedc J per QALY gainedc SBI scenario vs. current practice scenario 82 (35/140) 56 (24/94) 61 (48/70) 298 (146/514) 700 1,100 3,600 5,400 aDiscounted with 1.5%. bDiscounted with 4%. cQALYs and life years gained discounted with 1.5% and costs discounted with 4%. *Only SBI costs included. doi:10.1371/journal.pone.0005696.t002 Mean incremental costs per QALY are J5,400 for the SBI scenario compared to the current practice scenario. Mean incremental costs per life year gained are J3,600 for the SBI scenario compared to the current practice scenario. When only cost of SBI itself would be included in the denominator of the ICER, mean costs per QALY and per life year gained would be respectively J1,100 and J700,- for the SBI scenario compared to current practice scenario. Costs per QALY are higher than costs per life year gained in this scenario. This is because the number of QALYs gained falls short of the numbers of life years gained, since not all life years gained are lived in perfect health. Regarding the effect of the alcohol SBI in the long run, Figure 2 displays costs per QALY gained for different fractions of effect maintained in long run. The figure shows that costs per QALY decrease as the fraction of effect maintained in the long run increases. This is due to an increase in the amount of QALYs gained from a maintained reduction in alcohol consumption in the long run. It should be noted that if no effect is maintained at all in the long run, the costs per QALY gained would be infinitely high. Excessive Alcohol Use Figure 3 represents the Cost-Effectiveness Acceptability Curve for the SBI scenario, which displays the probability that the alcohol SBI is cost effective for different values of the threshold, i.e. for different monetary values placed on a QALY [14,20]. When, for instance, a QALY is valued at J5,000, implementing alcohol SBI is cost effective with a probability of 0.4. Alcohol SBI has a probability of almost one when the society is willing to pay J10,000 per QALY, which is well below the threshold usually placed on a QALY in the Netherlands (J20,000 per QALY gained). This means that alcohol SBI can be considered cost effective. Discussion Excessive alcohol use increases risks of many disorders, with associated losses of life-years and quality of life. Successful prevention of excessive alcohol consumption will therefore result in increased life expectancy and decreased health care costs. From a health care perspective, implementing SBI in primary care setting in The Netherlands would lead to health gains at a low cost. The cost-effectiveness of SBI was estimated at J5,400 per QALY gained and, thus, can be considered cost-effective. Effectiveness In several randomized studies, alcohol brief intervention has been proven to be effective in reducing excessive alcohol use [7,8,9,10,11]. However, Beich et al. [11] indicate that the numbers of patients needed to screen (NNS) in general practices is quite high to achieve benefits, because only two to three patients per thousand screened benefit from the laborious activities entailed in screening. But, we demonstrated that opportunistic screening is relatively cheap since all patients are already present in the waiting room of the GP. Cost-effectiveness Previous research studies investigating the cost-effectiveness of interventions similar to alcohol SBI also considered this type of intervention to be cost-effective [15,16,17,18,19]. However, these studies did not always express the outcome measure in terms of QALYs. Only Solberg et al. [15], when ranking the health impact and cost effectiveness of alcohol primary care intervention to reduce alcohol misuse did this in terms of QALYs gained. However, Solberg et al. [15] did not take into account the medical costs of diseases unrelated to alcohol in life years gained. Figure 2. Costs per QALY gained for different fractions of effect maintained in long run. doi:10.1371/journal.pone.0005696.g002 PLoS ONE | www.plosone.org 3 May 2009 | Volume 4 | Issue 5 | e5696