I have a set of data: [http://pastebin.com/KHLKD8XB][1] which is based on TVC (total viable counts - i.e., numbers of bacteria) from water going into a machine (BM), water taken from the machine (IM) and water taken from a device which is washed in that machine (Scope). library(ggplot2) testscope<-read.csv2("http://pastebin.com/raw.php?i=KHLKD8XB") testscope$date<-as.Date(testscope$date) ggplot(data=testscope,aes(x=date, y=tvc, colour=class)) + geom_step() + facet_grid(class ~ ., scales="free") + labs(title="Machine TVC versus Scope TVC") + ylab("cfu/100ml") Plotted using ggplot2: ![enter image description here][2] **My question is: How can I check whether TVC readings from the Scope are related to TVC readings from the machine ?** By eye, I can't discern a pattern between the machine level (IM) and the Scope levels. Note that although I have the BM data, that is not something we are particularly interested in at present - it is IM versus Scope that we need to understand. EDIT: Note that the dataset uses natural log, not base 10. My mistake. [1]: http://pastebin.com/KHLKD8XB [2]: https://i.sstatic.net/pksjL.png