At what price significance? The effect of price estimates on statistical inference in economic evaluation

Because data on resource utilization are now collected in many comparative trials of health interventions, statistical analysis of between-group differences in mean costs has become common. Statistical analyses of costs are generally performed conditional on a set of resource prices (or unit costs), thereby suppressing any uncertainty associated with those price estimates. Results presented here demonstrate that varying price estimates can have a non-negligible effect on statistical inference regarding between-group cost differences. Depending on the relative prices used in an analysis, between-group differences in total costs per patient may be either statistically significant or insignificant, regardless of whether differences in utilization of the underlying resources are statistically significant. These results highlight the importance of recognizing that evaluations based on patient-level economic data may be sensitive to assumptions regarding the values of unobserved variables, such as the relative prices of resources. Traditional methods of sensitivity analysis remain a valuable tool for analysing the implications of uncertainty around estimates of those unobserved variables.