Tide heights and rain averages are continuous. 8 bins were the maximum the function would allow me to use. The following is the call to
effect producing this plot:
R > plot(effect(term="rain.avg2:tide.avg",mod=bkrain9.lm,default.levels=8), main="", xlab="Precipitation - 24hr average (cm)", ylab=expression("TCB Concentration - CFU*100m"*L^-1),multiline=TRUE)
Plot updated. Could somebody explain the purpose of this plotting feature in context to predictor interactions?
Background: For a class project, I have created a linear regression model to evaluate the effects of the interaction between two predictor variables (tide height and precipitation) on bacteria concentrations.
Thermo-tolerant coliform bacteria concentrations were sampled at 5 sites in a day, where a sample time was recorded at sampling completion. I took an average of these for roughly 20 days, and calculated an associated 24hr average of precipitation before sampling completion, and a 50 minute (the sampling duration) average of tide height before sampling completion.