Here is an example of source material being summarized in a non-objective manner and a brief discussion of the writer interjecting a personal bias. An objective summary follows.
Original Source:
Other environmental costs include depletion of natural resources. It takes 4.8 pounds of grain to produce one pound of beef, Jim Motavalli reports in E Magazine. Animal feed corn "consumes more chemical herbicide and fertilizer that any other crop," Pollan writes, noting that the petrochemical fertilizer used to grow corn, he says, "takes vast quantities of oil-1.2 gallons for every bushel." The cow Pollan has bought "will have consumed in his lifetime roughly 284 gallons of oil." The industrial food system guzzles fossil fuels at a time when we should be conserving energy for the sake of our national security-and that of pristine ecosystems such as the Arctic National Wildlife Refuge.
--Excerpted from Mindy Pennybacker, "Why Fast Food Costs Too Much"
Non-Objective Summary:
In her leftist Green Guide article, "Why Fast Food Costs Too Much" Mindy Pennybacker reports that it takes 1.2 gallons of petrochemical fertilizer to grow one bushel of feed corn, making it the largest consumer of chemical herbicides among all industrial-farmed crops. Quoting tree-hugging writer Michael Pollan, she then points out, after first converting bushels to gallons, that a single cow consumes 284 gallons of oil before fulfilling its inevitable obligation of a once-in-a-lifetime pilgrimage to McDonalds. Concluding her environmental rant, she accuses the industrial food-production system of "guzzling" precious fossil fuel reserves at a time when we should be conserving energy.
This is an unfair summary: the writer's bias is clearly obvious. In this example, adjectives such as "leftist" and "tree-hugger" are derogatory labels deliberately expressing the author's low regard for Pennybacker's opinion.
Characterizing her opinion as an "environmental rant" is also deliberately belittling and the "pilgrimage to McDonalds" remark borders on editorializing, neither of which is appropriate in a summary.
Unfair labels and editorializing fall outside the boundaries of a summary for the simple reason that they add nothing new or helpful to the process of understanding the actual information. As a matter of fact, they get in the way, succeeding only in exposing personal biases.
Such distractions can lead the reader to question your motives and whether you are fully informed; to question whether your opinion is reasoned and credible.
In the revision below, the opinion of the writer has been removed and the summary succeeds in being far more objective. Notice that it is also much shorter.
Objective Summary:
In her Green Guide article, "Why Fast Food Costs Too Much" Mindy Pennybacker reports that 1.2 gallons of petrochemical fertilizer is required to grow one bushel of feed corn, making it the largest consumer of chemical herbicides among industrial-farmed crops. Using Michael Pollan's calculations to illustrate how conventional farming practices consume fossil fuels, she points out that a single cow, on a diet of petrochemically fertilized field-corn, will consume 284 gallons of oil in its lifetime.