CU [1]. These overheads of 15% were thus added to the calculated Erlotinib clinical costs. Data on cost-blocks were collected using the cost-block questionnaire [1]. In each hospital, the cost-block questionnaire was completed by the participating ICU and by one surgical and one medical ward. The annual ward cost was defined as the average of the costs of the two wards.Daily costs per patient were calculated based on the annual cost and the number of beds, assuming an occupancy rate of 100%. In fact, a large part of the total cost of care is represented by staff cost, which does not normally depend on occupancy.Between countries, costs were standardised to a common currency using Purchasing Power Parities (PPPs) rather than exchange rates, as the latter were designed to compare costs in financial markets which, unlike health service costs, change rapidly.
The World Health Organisation (WHO) PPPs were used because they consider health costs, are reported in many countries and are frequently updated [13]. The numeraire currency is the International Dollar, a theoretical currency based on what can be bought in each country with the US dollar [14]. In practice the International Dollar corresponds to the US Dollar and so the International $ is simply referred to as $ in this study. To aid interpretation in Europe we have also converted our results to Euros using the Dollar to Euro conversion rate in place at the end of the study; that is, $1.26 is equivalent to �1.00. We have also applied this conversion rate to other papers quoted in our manuscript where a Euro figure was not available.
Cost estimates for the cost-effectiveness analyses were adjusted for the same covariates selected in the analysis of effectiveness (age, Karnofsky performance status, indication for referral to ICU), and cost-effectiveness analyses were stratified by severity of illness (predicted mortality based on SAPS II).Cost effectiveness of ICU admissionThe cost effectiveness of ICU admission, compared with ward care, after ICU triage was evaluated using two measures; cost per life saved and cost per life-year saved. These were calculated at 28 days and 3 months after discharge for all admissions and represent the cost over and above ward care in relation to the benefit accrued.
Cost per life savedThe cost per life saved, or incremental cost-effectiveness ratio, is the difference in cost divided by the difference in mortality rates (absolute risk reduction), with the latter being calculated from the odds ratio derived from the adjusted analyses (see Additional file 1).Cost per life-year savedThe calculation of a cost Cilengitide per life-year saved requires an estimate of the life expectancy for survivors (see Additional file 1), information which was obtained from published data. Life expectancy of ICU survivors differs from that of the general population only for the first two [15,16] to four [17,18] years after hospital discharge. Thus, a hypothetical value of life expectancy was assigned to each patient usi