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Fallacies from Chapter 5 - 5469
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Fallacy
Unrepresentative Sample
Short Definition
over-generalize based on atypical observations
Long Definition
to draw a generalization on the basis of a sample that's not representative enough to be reliable.
Form
1st experience has X
2nd experience has X (these are not of varied types in general)
Thus, in general this type of experience has X
Keywords
none
How to Explain
State which types are not represented
Example
The teachers at SRJC are too tough since all the science and math teachers are too tough.
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1. The fallacy of unrepresentative sample involves wrongly generalizing about something based upon observations that are not typical enough to be reliable.
2. If a group has several sub-groups then the observations should entail most or all of these sub-groups.
3. Note that a small sample is almost always an unrepresentative sample unless the group has only one sub-group. For this class, you should name the fallacy unrepresentative sample if the sample size is large enough but does not adequately cover the various sub-groups.
4. An unrepresentative sample, which is sometimes named a bias sample, is a problem with some polls. This will be discussed later on the section about polls.
5. Unrepresentative Sample on the Internet
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1. The teachers at SRJC are too tough since all the science and math teachers are too tough.
Analysis: Unrepresentative sample because science and math does not adequately represent all of the various subjects taught at SRJC.
2. I received an 'A' on the first five tests in my English 101 class and tomorrow is test #6. Thus, I expect to get an 'A' on this test.
Analysis: Unrepresentative sample if test #6 covers a different type of material than the first five tests. If test #6 covers the same type of material as the previous tests, then the probability of getting an 'A' on test #6 is fairly high.
3. The meals served at Joe's Restaurant are excellent. I've been going there for lunch every Sunday for the last ten years and I've never had anything but a great meal.
Analysis: Unrepresentative sample to generalize about the meals at Joe's Restaurant because breakfast and dinner are not represented. Perhaps the Sunday cook is different than the cook on other days. If the conclusion had been 'The Sunday lunches served at Joe's Restaurant are excellent' then there would be no fallacy because the sample size is large enough.
4. Parking is not a problem at SRJC. I always find a parking space immediately for my two classes on Thursday night and Saturday morning.
Analysis: Unrepresentative sample since Thursday night and Saturday morning are not typical times where it would be difficult to find a parking space.
5. I have always received an 'A' in my math classes and next semester I'm taking Math 999. Thus, I should get an 'A' in that class.
Analysis: This actually happened to me. Unfortunately Math 999 turned out to be a very difficult class on pure theory, whereas my previous math classes were in practical applications. I received an 'F' in Math 999. Thus, my previous math classes did not adequately represent the different types of math.
6. A quality control engineer closely examines a random sample of automobiles produced on Tuesdays and Wednesdays at the Albany plant. She concludes that only 3% of all cars produced at his plant are faulty.
Analysis: Unrepresentative sample because cars were only examined on Tuesdays and Wednesdays, which normally are the days of the week in which workers perform their best.
7. I bought some bacon and a basket of tomatoes at Safeway. I expect the bacon to be fairly lean because what was showing through the package looked lean, and I expect the tomatoes to be good since the top layer of tomatoes looked good.
Analysis: Unrepresentative sample because what shows through a package of bacon and the top layer of a basket of tomatoes does not represent the rest of each item. The bacon inside may be very fatty and the rest of the tomatoes may be under ripe or over ripe.
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Last updated: 15:23 on 30 January 2013
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