Commentator: Most journalists describe their individual political orientations as liberal, and it is often concluded that there is therefore a liberal bias in current journalism.
Conclusion (however)
This is not the case. (i.e. There is not a liberal bias in current journalism)
Intermediate Conclusion (therefore)
Market pressures tend to keep sources of journalism like newspapers, magazines, radio, and TV impartial.
Evidence (because, since)
Those sources are all in the business of selling news and advertising, and maximizing profits requires targeting the broadest customer base possible.
Evaluate
Whenever we read Main Conclusion or Role paragraphs, we start by priming our brain with the reminder that, .
We train our ears to listen to that first sentence to hear if it's the author's opinion (in which case, it'll be the Conclusion). The other big pattern is that there's some claim or point of view attributed to someone else early on, and then the author pivots into a Rebuttal Conclusion with a classic pivot word like "But / Yet / However".
Structurally, the paragraph looked like this:
Most journalists say X, attribution / counterpoint / opposing premise
and it's often concluded therefore that Y. this is the opposing conclusion, supported by the first claim.
This is not the case, however the pivot word introduces the Author's voice. The rebuttal ("this is not the case") is the conclusion. We need to unpack / assign the pronoun "this" to what ever claim it was referencing.
because W, X, Y, and Z are businesses, the because (F.A.B.S) shows us that this is a supporting idea, supporting the "however" claim.
and therefore face market pressures the therefore tells us that this is a conclusion being drawn in part by support from the previous claim
since in order to maximize profits .. the since (F.A.B.S) shows us that this is a supporting idea, supporting the "therefore" claim.
We know that "there is not liberal bias" is the Main Conclusion, because this other conclusion is supporting the idea that "there is not bias".
Goal
We've done the hard part (finding the Main Conclusion). Now we just have to go find a match for "This is not the case", i.e "There is not a liberal bias in journalism".