Induction Induction general conclusion from incomplete evidence.

Transcription

1 Induction Induction is the process of drawing a general conclusion from incomplete evidence. You consider facts you have observed to draw a general conclusion about things you have not seen or heard..

2 Inductive Leap An inductive leap is the intellectual movement from limited facts (sample)to a general conviction. The reliability of your conclusion depends on the quantity and quality of your observations.

3 Daily Examples You use inductive reasoning everyday. For example, you inductively reason that the cashier at the grocery store is in a bad mood by the way she rings up items and deals with customers. If you notice that prices on the four items you bought in the campus bookstore are higher than similar items at a bookstore on the web, you may come to the conclusion that the campus store is a more expensive place.

4 The Sample Sample- the limited facts that you have. The sample must be... Known Sufficient Representative

5 Is the sample known? Does the sample lack evidence ("4 out of 5 doctors," UFOs, Big Foot, Atlantis, and other tabloid rumors or extravagant claims point to conclusive evidence that is unavailable. All of the former illustrations are examples of induction with an absent sample. Who are these doctors? What evidence backs the rumor? Who started the rumor? With UFOs and the like, it is claimed that the government is withholding crucial evidence, or the truth is beyond our each. If the sample is absent or unknown, you cannot reach a logical conclusion.

6 Is the Sample Sufficient? Using too little of a sample to reach a broad conclusion is stereotyping. This leads to the simplistic descriptions you hear about blacks, Jews, republicans, democrats, college professors, students, women, men, so forth and so on. This can lead to an inductive leap that is not warranted. Be suspicious of the words typical or average. Your average NFL player is a criminal. Look at Peterson and Rice. Your typical politician is a crook; just look at Illinois Gov. Rod Blagojevich.

7 Is the sample representative? A sample is unrepresentative when it is not typical of the whole class of things being studied. You cannot say most little league baseball coaches carry things too far, so competitive sports are bad for children; for instance, last night coach Smith set the opposing team s jersey on fire before the game in order to motivate his team. Coach Smith is not representative of most coaches; he is an atypical example (most coaches are more sensible than this).

8 Representative? An implied judgment may include everyone but the sample includes only a certain group. Watch for isolated statistics (all means all, not everyone followed be an isolated group). Obviously you cannot gauge America s attitude on universal healthcare by only polling the viewers of Fox News Channel because it primarily has a conservative audience. Often, polling is skewed to generate a particular outcome. Nevertheless, a small group can represent the larger population if all have an equal opportunity of being polled. The Gallup poll is mathematically sound according to the rules of probability. Its predictions are usually within 3% of the results. Any poll with a selective sample-where some individuals choose to respond to it and others do not is unrepresentative, since those who decide to respond cannot represent those that do not (hence magazine polls are often skewed 80% of those who have responded does not cover the whole population).

9 Representative? Some examples are less obvious. You cannot say women are better drivers based on accident statistics. The conclusion concerns all drivers, but the sample includes only those who have had an accident. To be representative the sample must include: Men Women Drivers who had accidents Drivers who had no accidents There are fewer women in accidents because there are fewer women driving automobiles. The argument sounds persuasive, but it is misleading because the statistics are isolated, thus meaningless until compared to all drivers.

10 Pictures are questionable Photographic evidence is usually unrepresentative since it is often staged or doctored for effect.

11 Occam s Razor Occam s Razor When a body of evidence exists, the simplest conclusion that expresses all of it is probably the best.

12 Occam s Razor Remember that the person with the motive and opportunity and gun is probably guilty. Conspiracy theories generally ignore the obvious, pointing to a shadowy figure as with Lee Harvey Oswald.

13 Occam s Razor The crop circles, which make neat pictures when viewed from the sky, were more likely created by people here on earth than aliens from outer space, which UFO enthusiasts claim (even after others have come forward to admit the hoax).