Experimenter Effect

<-NARRATOR:-> Now listen to part of a lecture in a psychology class.
<-MALE 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 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...