What procedure is used to calculate the trends?
Trends are calculated by applying the linear fitting model: summary.lm from the statistical Open Source package R. References: R-project website at http://www.r-project.org Chambers, J.M. (1992). Linear models. Chapter 4 of Statistical Models in S, eds. J.M. Chambers and T.J. Hastie, Wadsworth & Brooks/Cole. Wilkinson, G.N. and Rogers, C.E. (1973). Symbolic descriptions of factorial models for analysis of variance. Applied Statistics, 22, 392-9.