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In biology, hierarchical clustering is used to separate studied samples into different groups, thus if successful, the clustering criteria can be seen to "discriminate" between group A vs. B.

I am stuck trying to find an appropriate word to convey that two samples are so similar that they are "indiscriminable". It appears as that's not a word featured in dictionaries. I have tried "indiscernable" and that doesn't sound right either, neither does "inseparable".

What is a good adjective to use in this case? Should I try to rephrase my sentence?

PS: Please consider that this question refers to academic writing (in other words, "formal register" only).

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Indiscriminable has certainly been used. It seems a good technical word. – Andrew Leach Mar 8 '13 at 12:45
What about "almost perfectly analogous"? – rhetorician Mar 8 '13 at 15:03
@rhetorician not sure if that would be clear enough to the audience of the article. – posdef Mar 8 '13 at 15:06
up vote 3 down vote accepted

You are very likely looking for indistinguishable:

not able to be identified as different or distinct:
the counterfeit bills were virtually indistinguishable from the real thing

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is there a nuance difference between "indiscriminable" and "indistinguishable"? – posdef Mar 8 '13 at 12:51
@posdef Perhaps not in practice. But indiscriminable appears to be a word that people use because it sounds like it exists. Googling "hierarchical clustering indiscriminable" vs. "hierarchical clustering indistinguishable" should set the matter at rest. – coleopterist Mar 8 '13 at 13:02
Thanks, I accepted your answer as it addresses the question as it stands. I wonder however if there is another word I can use (it appears as one of my references use exactly that phrasing which I would avoid to duplicate). Does in-/non-discriminative fit, seeing as discriminative seems to be adjective form of "discriminate"? – posdef Mar 8 '13 at 13:23
@posdef No, I don't think that they are proper or commonly used words. The fact that oxforddictionaries.com/definition/english/discriminable is defined as being synonymous with distinguishable further strengthens the case for indistinguishable. – coleopterist Mar 8 '13 at 13:39
indistinguishable it is... Thanks again – posdef Mar 8 '13 at 13:42

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