Question

In a controlled experiment, ________.

A) the researcher has several hypotheses, one of which will be proven correct
B) the researcher knows the outcome before beginning the experiment
C) the researcher controls for the effects of all variables except one
D) the experimental organisms have all been used before and given good results
E) you need only a single experimental organism, which is tested again and again

Answer 1

C) the researcher controls for the effects of all variables except one

Explanation:

By definition, a "controlled" experiment is one that has as its only variable the variable of interest. All other variables are managed in such a way as to eliminate or cancel their influence on the outcome of the experiment. When the extraneous variables are managed in this way, we say ...

"the researcher controls for the effects of all variables except one"

__

Additional comment

Experimental controls are generally based on the experimenter's understanding of possible influencing factors. They generally do not take into account things the experimenter may not have thought of, or that the experimenter does not believe might have an effect.

One of the factors rarely accounted for is the effect of the experimenter's desire for a particular outcome. There is general disbelief that this has any effect on the results of an experiment. It is that disbelief that ensures it is not controlled for. ("Double-blind" studies notwithstanding.)