When a scientific researcher poses a research question, there generally is a null hypothesis and an alternative hypothesis for their question. For example, if a researcher wanted to compare two treatments for the flu, their null hypothesis is that there is no difference between the two treatments. The alternative hypothesis may be that treatment A is more effective than treatment B based upon what the researcher anticipates. However, when a researcher begin their experiment and does their analysis, they do so using the null hypothesis as their statistical standard and draw their conclusions based on the actual results. When journalists do their investigation, they often begin their equivalent to the alternative hypothesis, making their bias the leading factor in all facets of their journalistic process--their data collection technique, the analysis of those data, and the presentation of their results. Ultimately then, their research proves their bias. For example, 60 Minutes has a segment on Sunday looking at insider trading in Washington. Their segment highlighted a handful of Congress members who engaged in insider trading, land deals and the like. However, the segment included four Republicans and only one Democrat. To be sure, Republicans need to be held accountable for their unethical behavior and I most certainly don't want to let them off the hook, but why did CBS choose this unbalanced ratio of examples? Likely it is because this type of behavior among Republicans fit their "alternative hypothesis" based upon their bias. If researchers engaged in this kind of behavior, their research would be considered lacking integrity and would not be published. When "journalists" do it, it's commonplace.
When a researcher sets out to publish their results, the first part of their manuscript is their background/significance section where they describe why the research is significant and share other relevant information. Upon doing this, the researcher is required to cite their sources--whether it be a cancer prevalence statistic or the results of a previously performed study. The need for citing sources appears to be unnecessary for some journalists. Often, they "cite" anonymous sources only (see pretty much any article about the McCain/Palin campaign in October of 2008), where no sources in a story hundreds or thousands of words long is a proper noun. Heck, sometimes the only source they seem to have is a strawman, which seems to feed and perpetuate their bias.
If a researcher's project gets funded--be at from a non-profit, the government, industry, or their own institution--they are required to note their funding source, and they are also required to report any conflicts of interests that may exist. I remember doing the literature review for my master's thesis which was on caffeine consumption and depression when I ran across an article on the effects of drinking soda where the researchers concluded that soda was a reasonably benign beverage. However, I noticed that the study was funded by Coca-cola. This isn't to say the data and results were biased necessarily to indicate the effects of soda were neutral or benign. The study had been peer-reviewed. However, at least those reading the piece were aware of where the funding came from and that possibly the results could be skewed toward the liking of those funding the research. If a researcher is a consultant for a drug company, that is known as well. However, in journalism such informational tidbits are not readily known to the average American. The average American may not know that George Stephanapolos once was President Clinton's press secretary, yet he is working as a "journalist", not a commentator. It is not readily known that, although they are managed independently, there are funding ties between federally subsidized GE and MSNBC. If a researcher leaves out their citations, funding source, or conflicts of interest, they don't get published, yet for "journalists" is just another day at the office.
Striking the balance between idealism and realism while attempting to not become overly cynical is hard when it comes to today's journalism. However, what is required of scientific researchers as a matter of solid research principles, integrity, and ethics, is tossed by the wayside by many journalists. I don't want to lump everyone in that category; there are a rare few who understand the core of real investigative journalism. Scientific research is not without its own faults and failings itself--both in method and ethics. It mush be said though that it would go along way for the reputation of political journalism if they held themselves to the same standards as research scientists do as a matter of both principle and career success.