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Because
prescriptions of NSAIDs show seasonal behaviour, changes in costs per prescription (as a
secondary variable) were also evaluated with a determinist time series analysis. The
object of this analysis was to find a function to serve as the analytical representation
of a set of data that evolves over time with reference to an imaginary line. As in any determinist time series analysis models of the
functions available, the S or Gompertz curve was selected (figure 3). Its analytical
expression, similar to lineal regression, is: y=exp(a+b/t)); where a: the constant for the
model, b: the slope y t: time. This model best adjusts to the empirical data for the 12
months before intervention, calculated with the r2 coefficient of determination and
Snedecor's F test. |
