The table below gives the concentration of total polycyclic aromatic hydrocarbons (PAHs) in three benthic sediment cores taken 3 km, 2 km and 1 km from an oil refinery situated on the edge of an estuary. (a) Analyse the data as a two-factor ANOVA without replication, using depth and distance as factors. Is there a significant effect of distance? Is there a significant effect of depth in the sediment? (b) The environmental scientist who collected these data mistakenly analysed them with a single-factor ANOVA comparing the three different cores but ignoring depth (i.e. the table below was simply taken as three columns of independent data for three samples). Repeat this incorrect analysis. Is the result significant? What might be the implications, in terms of the conclusion drawn about the concentrations of PAHs and distance from the refinery, if the incorrect single-factor analysis were done?
