We can not say with 100% certainty that a particular set of data fits in either group. This is more of an AI problem than a statistics problem, although in thi

We can not say with 100% certainty that a particular set of data fits in either group. This is more of an AI problem than a statistics problem, although in this particular case the differences between the two types of data sets is big enough that a relatively crude statistical analysis can generate a cleat answer to the question. In a more general sense, I would tend to use a Self Organising Map (http://en.wikipedia.org/wiki/Self-organizing_map http://en.wikipedia.org/wiki/Self-organizing_map) to identify the two groups of data, and then discrimante between them. The dimensions of the SOM would be different statistical analyses of the data sets - what is the mean, the absolute spread, the standard deviation, the median, etc. The nice thing about using a SOM is that it will show you whether or not you have succeeded in finding a measure that can successfully discriminate between different data sets - whilst at the same time actually doing the discrimination for you.