TRIM generates additive and multiplicative parameters. Which are to be preferred?
These parameters are different descriptions of the same estimates: the additive parameter is the natural logarithm of the multiplicative parameter. So, it does not matter which one to use, but the multiplicative parameters are easier to understand. The multiplicative trend reflects the changes in terms of average percentage change per year. If the trend is equal to 1, than there is no trend. If the trend is e.g. 1.08, then there is an increase of 8% per year. If the trend is 0.93, then there is a decrease of 7% per year.