Relies on a sample that it is reasonable to suppose is unrepresentative of the group about which it draws its conclusion. Hi Ruaner, This is a little difficult without knowing the full context in which that sentence has been placed. However, I believe it is suggesting that, whatever data, information or result (sample), which it is speaking about, the author seems to indicate that they believe this "data" does not truly represent the group in which the conclusion is referring too. Even though it is apparently speaking about that particular group. Hope this helps

Let's build this sentence one piece at a time. First, whatever subject is being talked about is not part of your sentence. So the sentence really begins with: > (The subject) relies on What does it rely on? A sample. > (The subject) relies on a sample What is important about the sample? It is unrepresentative. In other words, it does not properly represent. > (The subject) relies on a sample that is unrepresentative What does the sample not properly represent? The group > (The subject) relies on a sample that is unrepresentative of the group At this point, add the phrase "it is reasonable to suppose". Which changes the sentence from a definite statement, to more of an opinion. Or a hypothesis. The writer is saying that "the sample is unrepresentative" is a possibility to think about. > (The subject) relies on a sample that, it is reasonable to suppose, is unrepresentative of the group Finally, which group is the writer talking about? "the group about which it draws its conclusion". The word "it" refers to the subject. So rewrite this as "the group about which (the subject) draws (the subject's) conclusion." This phrase has the same meaning as "(the subject) draws its conclusion about the group". The word "which" is used because "the group" comes before "the subject", not after. > (The subject) relies on a sample that, it is reasonable to suppose, is unrepresentative of the group about which (the subject) draws (the subject's) conclusion. In summary, the Subject uses a sample to draw a conclusion about a group. The writer of this sentence thinks that the sample is a bad one, because it does not represent the group. So the writer believes the conclusion has not been proven. The writer disagrees with the Subject, but makes it clear that their disagreement is a possibility/opinion.

There are two issues with this that create ambiguity: (a) there is no explicit subject for the main verb "relies", and (b) it is not clear what the antecedent of the second "it" is. I would guess that they are actually both the same, and refer to an article in a journal or magazine that the writer of your sentence is commenting on. Assuming so, and marking the parenthesis explicitly, this sentence rendered in full would read: "This article relies on a sample that (it is reasonable to suppose) is unrepresentative of the group about which the article draws its conclusion."