PubMed · 11968969
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N Walsh, J Huntington. Testing the pilots.. https://pubmed.ncbi.nlm.nih.gov/11968969/
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The usual implementation of contingent valuation (CV), in the context of priorities setting for allocation of public funds in health care, is to develop as many surveys as there are programmes, i.e. to perform separate evaluations (SE). In the EuroWill project, three health programmes (for heart disease, breast cancer and a service of helicopter ambulance) were however simultaneously evaluated, i.e. a joint evaluation (JE) was performed. The paper examines the issue of the econometric techniques that should be used to estimate WTP values obtained in the context of JE by comparing the application of independent OLS regressions for each programme versus simultaneous estimations using seemingly unrelated regressions (SUR) on data of the French EuroWill survey. It shows that separate estimations may lead to misspecifications because they cannot take into account that JE exogenously provides a reference structure to the respondent which affects the estimates of WTP for each programme. Therefore, the potential advantage of JE versus SE as an elicitation technique in CV studies applied to health care (to better control the referents used by respondents for evaluating different programmes) only holds if simultaneous rather than independent techniques are used in the estimation of WTPs.
The objective of this study was to derive a simple equation to convert distances between air miles traveled by a helicopter and ground miles traveled by an ambulance. We performed a retrospective analysis of a convenience sampling of 245 "lights and sirens" ground ambulance transports between 1993 and 1997. Ground distances were recorded from odometer miles for each transport. Air miles were calculated using the Global Positioning System (GPS), measuring the distance in a straight line from the scene to the hospital. Air and ground distances were entered into a computerized spreadsheet, and the correlation coefficient and regression equation were derived. A simple approximation equation was developed and compared against the derived regression equation. There was a strong linear correlation between ground miles and air miles at virtually all distances studied (R = 0.932, R(2) = 0.869). Regression analysis revealed the following relationship: Ground miles = 0.94 + 1.25 (air miles). This was simplified to an approximation of: Ground miles = 1.3 (air miles). The approximation equation yielded an answer within 1 mile of the regression equation for distances up to 40 air miles. It is concluded that in a mixed rural and urban EMS system, one may convert air and ground mileage estimates by using the simple relationship: Ground miles = 1.3 (air miles). This conversion coefficient may prove useful for EMS personnel in designing reasonable helicopter utilization policies, making accurate transport decisions and conducting research.
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