Psychology is a science, so that means that Psychologists will
often use experiments to gather data and learn more about what they are studying.
But not every study is an experiment. So, let s take a look at what an experiment is
and isn t so that you can spot an experiment from the jumble of other research approaches.
In simple terms, an experiment is a research method where causal conclusions can be drawn,
because an independent variable has caused a change in a dependent variable.
Too many variables ?! I can make it simpler! An experiment can tell us if A
can cause B. For example, if I press the light switch, will the brightness of the room change?
I control the light switch that s my independent variable and then I measure
the effect it has on the dependent variable in this case the brightness of the room.
It s a silly experiment, but let s give it a go. The lights are currently on, and now I ll
manipulate my independent variable the status of the light switch and see what happens.
Hello? Err. Hello? Oh! Hello! Well, surprise-surprise! In
this experiment we discovered that the light switch does indeed have a causal
relationship with the brightness of the room. Many classic studies in Psychology are also
experiments and their experimental design is pretty similar to our light switch experiment
once of the details are stripped back and we just look at the research method itself.
Let s take a look at a couple and see. Solomon Asch s famous line comparison
study examines the role of social influence on a person s public behaviour. Asch had
stooges actors perform the role of other participants in the study and told them what
to say. Because Asch was controlling the stooges behaviour, this is his independent variable.
Asch wanted to see if the behaviour of the real participant changed BECAUSE
of the stooges behaviour. Therefore, the real participant s behaviour is the dependent variable:
dependent on the stooge in this case. Peterson and Peterson (1959) used the experimental
design for their study on the duration of short-term memory. Each of their 24 participants
was presented with a consonant syllable and a three-digit number. They were asked to recall this
information after a retention interval of 3, 6, 9, 12, 15 or 18 seconds. Therefore, which variable
are the researchers independently manipulating here? /// Time! The retention interval
is the independent variable. The dependent variable in this study is how much
the participant is able to recall because their ability to recall the nonsense syllable and number
is dependent of the amount of time that has passed.
An important feature of experiments is standardised procedures.
This is because a key quality of scientific investigation is that it should be replicable. And
in order to repeat and replicate, we need to know exactly what we re repeating and replicating.
Returning to the Peterson and Peterson study as an example, the researchers specify exactly
what they are showing their participants three consonants followed by three numeric
digits. Super specific. Easy to copy and replicate. Not letters and numbers , not
something to remember , but specifically three consonants followed by three numeric digits, in
written form. And the independent variable of time isn t left as a vague reference to
time will be left in between showing participants the code and asking them to recall it , no!
The researchers set a standardised procedure, which dictates exactly how many seconds will be
left between presentation and recall. Anyone can pick up Peterson and Peterson s methodology and
clone their experiment and their results should end up pretty much identical too.
Finally, a critical consideration for any researcher designing an experiment
is how to control for extraneous variables. Extraneous variables are other changing
conditions that might influence the dependent variable, muddying the findings of the study.
Imagine if half of the participants conducted an experiment at 10am and the other half at midnight
maybe the time of day could unintentionally influence the results. Background noise
is another common factor that psychologists consider in the design of their experiments.
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