If you have two groups
... each group would
have the same amount
of boys as girls. They
would do different things
but they would be match
for example same levels
disadvantages - Very time
consuming and difficult to match
all of your participants in this way
It is impossible to match people for all characteristics
even if you were to use MZ twins between the two
groups! There would be extraneous variables
advantages: No order
effects since each
participant only does the
You can use the same material twice
Groups are similar in terms of individual characteristics
Repeated measures design
Use the same participants in each group or condition
advantages - The two groups have the same age, sex,
personality, ideas, past experiences, IQ, reaction times
(crucially for this one) etc. They are perfectly matched.
They are the same people!
Disadvantages - Order effects: Assuming, as we
expect the group do better on the second day, can
we be sure that this increase in performance is due to
the coffee? It could be that they’ve had the chance to
practice the task the day before! It’s not surprising
they’re better the second time around. This is called
order or practice effect.
course, on some
tasks it could work
the other way, and
a task done the
second time shows
because they’re fed
up with doing it.
Independent measures design
Different people allocated to different groups
therefore two groups can happen at the same
Disadvantages: Participants are not matched in terms of IQ, personality, age etc.
You will need twice as many participants.
Advantages: No order or practice effects
Can use the same stimulus material (such as word
lists in memory) for each group