Data Set 1A: Algal Photosynthesis vs. Salinity and Temperature

These data are from a controlled experiment in which two quantitative variables were manipulated, to determine their effects on the quantitative response variable. Both explanatory variables therefore are of direct interest; there are no supplemental variables and there is no need for reduction of variables. The study used a balanced factorial randomized design. Three levels of one explanatory variable, and four levels of the other, were used in all 12 possible combinations, with three replicates of each. In such a design the two manipulated variables are perfectly uncorrelated so that there is no confounding between them. The model used to analyze these data is fairly simple, including only linear terms for both explanatory variables and their interaction. (These data are a subset of the data from the actual study, chosen so that this simple model is suitable. Analysis of the full data set, presented in handout 1B, includes polynomial terms to model nonlinearity.)