1) The SI model is a formula adapted from Fisher's ideal index formula (Spiegel, 1992) which employs the weighted aggregate technique to estimate changes in quality or quantity are follows:
It is arguable that the means of projected PPM output values enumerated in Table 3 should suffice as the PPM suitability indices of the Ficus species studied, and that there might be no need for the rigours of computing the Si's with Fisher's ideal index formula.
First, the data on expenditures required for computation of either Fisher's Ideal index or the Tornqvist index are available only at the quarterly frequency.
Just as it is not possible with existing source data to calculate the textbook version of the Laspeyres index, so it is not possible to calculate the textbook versions of either Fisher's Ideal index, the Tornqvist index, or a geometric-means index.
As expected, the geometric price index increases less rapidly than does either the Tornqvist index or Fisher's Ideal index. In other words, the unit elasticity of substitution implicit in the geometric formula appears to overstate the extent to which consumers respond to changes in relative prices at the upper level of aggregation.
In both the fixed-base and the chainweight contexts, die Fisher's ideal index and the Tomqvist index may be constructed.
The fixed-base (F.sub.t,r) and chain-weighted (f.sup,c.sub.t,r) Fisher's ideal indexes are given by:
To examine this issue, we have used 1992-94 CE Survey shares for each population group in our study to construct the Paasche and Fisher's ideal indexes
shown in table 6.
namely, the Tornqvist and Fisher's Ideal indexes
, under a chain as well as a fixed-base specification.