Official 15 Task 3
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Experimenter Effect
 

One objective of any experiment is, of course, to obtain accurate results. Sometimes, however, problems occur that lead to inaccurate results. One such problem is the experimenter effect. The experimenter effect occurs when a researcher’s expectations affect the outcome of the experiment. The researcher expects a particular result from the experiment, and that expectation causes the researcher to act in ways that influence the behavior of the experiment participants, thereby invalidating the results of the experiment.

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Narrator: Now listen to part of a lecture on this topic in a Psychology class.
Professor: For example,
I recently read about a case in which a researcher was given two groups of monkeys.
And he was asked to train these monkeys to pick up a ball and put it in a box.
And he was told to record how many hours it took to train each monkey to learn to do this.
Now, before he started the training,
the researcher was told that one group of monkeys was highly intelligent,
and that the other group was less intelligent.
In truth, there was no difference between them.
All the monkeys were actually very similar in terms of intelligence.
But the researcher didn't know that.
He thought one group was smarter,
so he expected that that group would be easier to train.
So what happened? Well,
the researcher trained the monkeys to perform the action,
and it turned out that, on average,
it took him two hours less time to train the supposedly smart monkeys than the supposedly less intelligent monkeys.
Why? Well,
it turns out that with the supposedly smart monkeys,
the researcher smiled at them a lot, gave them a lot of encouragement,
talked to them a lot, worked hard to communicate with them.
But with the monkeys he thought were less intelligent,
he wasn't as enthusiastic.
He didn't try quite as hard, wasn't quite as optimistic.
Question
Explain how the example from the professor’s lecture illustrates the experimenter effect.