The semi-attached figure is described in Darrel Huff's "How to Lie with Statistics" as, "If you can't prove what you want to prove, demonstrate something else and pretend that they are the same thing." By pretending the unrelated figure proves your point, you avoid having to provide actual evidence for your claim. These are also called irrelevant conclusions.
News outlets sometimes use the semi-attached figure to make a news story seem bigger then it actually is. For example, a news article states that airplanes grow increasingly dangerous because the number of airplane-related deaths last year was many times more than the number of such deaths in 1910. While the statistic is technically true, it is misleading because it is irrelevant. Airplanes had only recently been invented in 1910 and so it is not accurate to conclude that flying is more dangerous based on that figure.
Politicians use a variety of propaganda and debating techniques, including the semi-attached figure to get their political points across, without having to prove them. For example, if a politican stated that the U.S. spends billions of dollars on foreign aid every year while complaining about deep budget cuts, it could sound like foreign aid makes up a huge amount of the budget. However, it actually makes up only about 1 percent of the federal budget.
Semi-attached figures are most often related to infomercials, although they can be found in other commercials as well. If an advertisement states that more people use one brand of aspirin than any other brand combined and then invites viewers to conclude that this brand of aspirin must be superior. Although more people may use that brand, that does not prove it is the best out there.