Health status index: category rating versus magnitude estimation for measuring levels of well-being.

Levels of Well-Being are social preferences, or weights that members of society associate with time-specific states of function. A Weighted Life Expectancy, which can be used to measure program outputs, is created by summing the levels across diverse cases and multiplying them by probable transitions (prognoses) among the states and levels. This operation requires however, that the Levels of Well-Being be measured on underlying metric scale. The present analysis compares preference measurements from a simple category rating procedure with those obtained using the more complex and difficult magnitude estimation method which has been claimed to yield ratio level measures. In a randomly counterbalanced design, 65 college students rated 30 case descriptions representing the range of the Well-Being continuum. The results exhibit the classical logarithmic relation observed for a prothetic continua. When transformed to a meaningful 0-1 unit scale, however, the magnitude responses are compressed at the lower end of the scale near death. Such results are inconsistent not only with category rating, but also with intuitive notions of the relative importance of the function states, with the results of rating procedures that simulate social choice, and with evidence that confirms the interval properties of the category ratings themselves. Furthermore, the ease of administration of category rating means that multiple attributes of cases can be considered jointly, avoiding the need to aggregate scale values for different attributes by arbitrary rules. In sum, magnitude estimation is inappropriate as a measurement method for a Health Status Index and is probably also inappropriate for other measures of utility and social choice.