Transformations of the purely multiplicative time series
model will either remain the purely multiplicative model or the additive
time series model. These transformations are required to meet the variant
assumptions on either the multiplicative or the additive models with respect
to the seasonal component. When these assumptions are met, a transformation
is regarded as being successful with respect to the seasonal component.
This study deals with the methods required in the determination of intervals
for the seasonal indices for successful transformations. Intervals derived
are found to lie in the neighbourhood of 1.0. Numerical examples are used
to illustrate the results obtained.