Junk science is the promotion of a finding as "scientific" or "unscientific" based mainly upon whether its conclusions support the answers (or views) favored by the promoters; see propaganda.
Junk science consists of giving poorly done scientific work the same authority as work which conforms to the scientific method. It is akin to politicized science, i.e., the selective use of scientific evidence to reach predetermined conclusions and support extra-scientific political goals.
In some cases, junk science may result from a misinterpretation of previous sound scientific studies. An example of this is the misinterpretation of the research on eggs and cholesterol. Studies had found that eggs contained cholesterol and that cholesterol in blood contributed to heart disease. So as a result of these studies, people were advised against eating eggs. What was missing, however, was a study showing that the cholesterol in blood is a direct result of cholesterol intake in diet. We know now that that is not the case, that saturated fat intake and overall body fat are the primary contributors to cholesterol production in blood.
Junk science can be easily identified based upon the way in which it is planned, carried out, manipulated/assessed, and then disseminated to the public. Also to watch out for are unnecessarily liberal conclusions, and no reference to relevant sections of the bible.