TRIM (TRends and Indices for Monitoring Data; freeware program developed by Statistics Netherlands to be applied in wildlife statistics; Pannekoek & Van Strien, 2001) is the standard software tool we use to analyze time series of count data obtained from monitoring schemes and to produce estimates of yearly indices and trends. The analysis is based on log-linear Poisson regression (a form of generalized linear modelling). Such analyses are also available in standard statistical packages, but because TRIM is tailored to a selected set of models only, it runs faster and is easier to use.
The latest version of TRIM is TRIM 3.54 (released in 2006), designed to run under 32-bits versions of Windows, as Windows98, Windows2000 and WindowsXP. However, the old version of TRIM developed originally in Delphi has been outdated for some time and couldn´t be updated anymore. Hence, the need for developing TRIM in a new platform became essential. Therefore, TRIM has been developed as an RTRIM package and modified for PECBMS needs into the RTRIM-shell.
RTRIM-shell is a set of three R-scripts developed by Statistics Netherlands, using the RTRIM package to calculate national species indices. RTRIM-shell is determined to calculate national species indices sent to the PECBMS coordination unit; therefore, it is modified to the PECBMS use. We therefore strongly recommend using the RTRIM-shell. PECBMS plans to leave the TRIM and Birdstats in the near future and to use only RTRIM-shell for the national index calculation.