1 29-13 common fallacies

Common Fallacies

Dr. John Bradford

Common Mistakes in Social Research

1. Contamination2. Fallacies of presumption

– Hasty Generalization– False Dichotomy– Spurious association– ‘Post hoc’ fallacy

3. Fallacies of the wrong level– Ecological Fallacy (group to individual)– Reductionist Fallacy /Fallacy of Composition (individual to

group)

4. ‘Ad Hoc’ Fallacies

I. Problem of Contamination

• Suppose that there is so much heat given off in the first test tube, Y₁ that it spreads and heats up Y₂ . This is contamination!

• The Error of Contamination occurs when the social researcher acts as if the influence of an independent variable is restricted solely to experimental group when in fact it is also influencing the ‘control group’.

Y₁ Y₂ Influencing the control


• One cannot assume that a change in an independent variable (X) affects the dependent variable (Y) only in those settings where the independent (X) variable is present or has changed.

• Why? Because people observe what happens elsewhere. The mere existence of some X in some setting, may affect Y in other settings where X isn’t present, or has changed.


Example: Sweden v. Norway

• The effect of Norway’s entrance into World War II (X) on fertility rates in Norway (Y₁), using Sweden (Y₂) as a control.

• An invalid inference might be: “If Norway had not been invaded in 1940, its fertility rates would have been like Sweden’s at that time”


Example: Sweden v. Norway

• One problem (among many) is that Sweden is not a good ‘control’, even if it is exactly like Norway in all other conceivable characteristics, and even if it was an exact replica of Norway.

• Because Sweden was also affected by the Nazi invasion…

II. Fallacies of Presumption

1. Hasty generalization: making a general conclusion based on too little information– My former husband was a jerk…from that I learned

that all men are jerks.

2. False Dichotomy (also called “False Bifurcation”, “Black and white fallacy;” “either/or fallacy” “False dilemma.” ): involves turning a complex issue into one that has only two choices that are opposite of one another– ‘You are either with or against us!’


3. Fallacy of false cause (spurious association)– It says (wrongly) that if two things are associated,

then one of them must be the cause of the other. If A and B are associated, then A must cause B.

– Example: More and more young people are attending high schools and colleges today than ever before. Yet there is more and more juvenile delinquency among the young than every before. This makes it clear that these young people are being corrupted by their education.


3. Fallacy of false cause (spurious association)

• ‘Post hoc’ fallacy: a more specific form of spurious association, which asserts that, if A occurs before B, then A is necessarily the cause of B.– Derived from the Latin phrase,“Post hoc, ergo propter

hoc” (Latin: After this, therefore because of this).

– Example 1: 98% of Heroin users started off with marijuana. Therefore, marijuana smoking causes people to go on to the hard stuff.

– Even more drank alcohol, and 100% drank water! Only about 1% of marijuana users end up using heroin.


3. Fallacy of false cause (spurious association)• ‘Post hoc’ fallacy:• Example 2: Dr. Manfred Sakel discovered in 1927 that

schizophrenia can be treated by administering overdoses of insulin, which produced convulsive shocks. Hundreds of psychiatrists drew a faulty conclusion and began to treat schizophrenia and other mental disorders by giving patients electric shocks without insulin. So, they skipped the insulin but went to shocks. At a psychiatric meeting some years later, Dr. Sakel sadly came forward to explain that electric shocks are actually harmful, while insulin treatment restores the patient’s hormonal balance. The doctors had confused the side effect with a cause.

III. Fallacies of the Wrong Level

• Ecological fallacy: studying something with the group as the unit of the analysis and making inferences about the individual

– Group Individual

• Reductionistic fallacy: studying something with the individual as the unit of analysis and making inferences about the group

– Individual Group


Ecological fallacy: (inferring lower from higher levels, or parts from wholes)

• Example 1: In the United States presidential elections of 2000, 2004, and 2008:i. Wealthier states tended to vote Democratic ii. Poorer states tended to vote Republican. iii. Yet wealthier voters tended to vote Republican

and poorer voters tended to vote Democratic.

• The error would be to assume that, because wealthier states voted Democratic, wealthier voters also tended to vote Democratic.



• Example 2: In American cities, there is a strong relationship between illiteracy rate and proportion of people who are foreign born. Does this association hold for individuals? No, it could be that all the foreign born are highly literate, they just gravitate to urban areas where there are also lots of native born people who are illiterate.



Example 3:

• Suppose you flip 10 unbiased coins 5 times.

• A count of all of the coin tosses will be pretty close to 25 heads and 25 tails or 50-50%.



Example 3:

• Some coins, however, will have more heads than tails, others will have more tails than heads, for entirely random reasons.

• We cannot infer from the overall distribution of heads and tails (50-50%), the specific distribution of heads and tails for each coin!


Reductionist Fallacy (aka Fallacy of composition): (inferring higher levels from lower levels, or the whole from the parts):

• Example 1: ‘Paradox of Thrift.’ Saving is good for an individual, but not necessarily for the economy as a whole, because lack of spending in the aggregate can cause a recession.

• The error would be to assume that what individual interest necessarily coincides with collective or aggregate welfare.


Reductionist Fallacy (aka Fallacy of composition): (inferring higher levels from lower levels, or the whole from the parts):

• Example 2: ‘Dream Team’: Consider the study of basketball. Suppose you gather together the best players in the world. Does this mean that your team will naturally be the best? Not necessarily. (All these great players might have such great egos that they can’t manage to play together; a team of mediocre players might click so well that they are unbeatable as a team).

IV. Non Sequitur

• Non sequitur fallacy (non-SEK-wa-tuur): the term is Latin for “it does not follow.”

• In logic, the term is used to indicate a conclusion that can not be justified by the premises or evidence offered in an argument. In other words, the non sequitur fallacy occurs when an the conclusion does not follow from the premises.

IV. Non Sequitur

Argument A:(1) Most poor people don’t commit crimes(2) Some rich people commit crimes• Therefore, there is no relation between poverty

and crime!Argument B:1. Most people with bullet wounds don’t die.2. Some people without bullet wounds do die.• Therefore, bullet wounds are not a direct cause

of death. ?????

1 29-13 common fallacies

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