|
|
Experimenter Bias |
| Description: | ||
| The argument draws a conclusion from data that has been influenced by the expectations and hopes of the person collecting the data. | ||
|
|
||
| Comments: | ||
| In most cases this influence is unconscious and unintentional. Bad data may be due to such "honest" mistakes as rounding up or rounding down to favor a certain result, or treating ambiguous results as favoring the preferred result. However, there have also been documented cases of outright fraud. | ||
|
|
||
| Examples: | ||
| Samuel Morton collected data on cranial capacity, hoping to prove that white races had a larger brain size than dark races. He measured cranial capacity by filling the cranium with mustard seed and measuring how much seed each skull could hold. He performed the experiment himself, knowing which skulls belonged to whites and which belonged to blacks. His results confirmed an average cranial capacity of 87 cubic inches for whites, but only 83 cubic inches for Africans. | ||
| In 1955 Cyril Burt published a study of 21 identical twins who were separated at birth and raised in different families. His study clearly showed that intelligence and behavior is controlled more by genetics than by environment. [It was later discovered that Burt's data was fabricated, and indeed that many of the pairs of twins included in his study did not even exist.] | ||
|
|
||
| Discussion: | ||
| Since such tainting may be unconscious, steps must be taken to prevent it.
The fallacy of Experimenter Bias may be avoided by using "double blind"
techniques, so that experimenters do not know (as they are recording data) which result
the data favors. Any experiment that does not employ such techniques may be suspected
of committing the error of Experimenter Bias, so experimenters are generally very careful
to build such techniques into their experiment. Double blind means that both the experimenter and the experimental subject are "blind" to the meaning of the data being collected. Experiments in which the experimenter is not "blind" may commit the fallacy of Experimenter Bias; experiments in which the experimental subject are not "blind" commit the fallacy of Tainted Sample. By the way, Samuel Morton later re-did his measurements, using lead shot rather than mustard seed, and having lab assistants perform the measurements without knowing which skulls were in which group. The revised measurements showed no average difference. (See Stephen Jay Gould's The Mismeasure of Man for a complete account of the story as well as of Cyril Burt's fabricated twin studies.) |
||
|
|
| Classification: An Error in Observation (an inductive fallacy of soundness, with a falsehood in the major premiss). | ||
|
||
| Source: Certainly not the original source, but the most entertaining and comprehensive discussion of this fallacy is in Stephen Jay Gould, The Mismeasure of Man, New York: Norton, 1981. | ||
|
||
Go to: WELCOME EXPLANATION of PRINCIPLES TABLE of FALLACIES EXERCISES INDEX