I'd like to see if one group, taken from the start of the time frame, has a significant difference or similarity to another group, which represents the remainder of the time. This may be a total nonsensical thing to do however when I graph the averages of my data, the data is higher at the start than at the end and I would like to know if this is significant at all.

I've posted my data here if anyone wants to take a look:

http://pastebin.com/CNjuskFP

and I've been advised to use kendall's tau, however I'm unsure if this is correct. I'm also unsure about what information to post here so any help on that would also be massively appreciated.