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Research Methods
Lesson 02: Experimental Design
Task 1: Designing an experiment…
Starter: Design an experiment to test the following:

You want to investigate gender differences in the speed of texting
on mobile phones in order to see who are the fastest, males or
females.
Make sure you consider everything you have learnt about Research
Methods (RM) so far…

Aim – Your research question?


Your operationalised IV & DV
Method – Including:

The Design (Laboratory, Field)

Participants (Sample)

How will you recruit your participants? How will you
divide your participants in the study?

Materials required

The procedure
Make sure you can explain all of your choice – you need to be able to
justify why you experiment is the best!
Learning Objectives:
Compare & contrast the following experimental designs:

Independent group design

Repeated measures group design

Matched pairs group design

Identify which experimental design is used within
psychological research.

Detail the advantages & disadvantages of different
experimental designs.
What is meant by experimental design?

If you have decided that an experiment is the best
approach to testing your hypothesis, then you need to
design the experiment.

Experimental design refers to how your participants
are allocated to the different conditions in an
experiment.
Experimental Design…
Experimental design refers to how we use/allocate our
participants in our experiment.
There are three main ways that participants can be
allocated:

Independent measures

Repeated measure

Matched pairs
These Jelly Babies are
now your participants…
Independent Measures

Different participants are used in each condition of
the experiment.

This should be done by random allocation, which
ensures that each participant has an equal chance of
being assigned to one group or the other.

Independent measures involves using two separate
groups of participants; one in each condition.
Independent Measures
You want to test how noise will affect concentration in a
reading test.
Group 1
Group 2
Concentration on
a reading test.
Task 2: Arrange your Jelly Babies to test the above
statement, allocating your ‘participants’ according to an
independent measures design…
Independent Measures
Participants
Condition 1
A
B
C
D
E
Participants
Condition 2
F
G
H
I
J
Concentration on
a reading test.
One the mini-whiteboards,
detail one strength and one
weakness of using an
independent groups design.
Advantages & Disadvantages
ADVANTAGES:

Avoids order effects (such as practice or fatigue) as people
participate in one condition only. If a person is involved in
several conditions they man become bored, tired and fed up by
the time they come to the second condition, or become wise to
the requirements of the experiment!
DISADVANTAGES:

More participants are required and therefore the design is more
costly and time consuming.

Differences between participants may affect results, for
example; variations in age, sex or social background. These
differences are known as participant variables (i.e. a type of
extraneous variable).

Were all of your Jelly Babies the same in terms of age, sex,
social background…
Repeated Measures

The same participants take part in each condition of
the experiment.

This means that each condition of the experiment
includes the same group of participants.
Repeated Measures
You want to test how noise will affect concentration in a
reading test.
Group 1
Group 2
Concentration on
a reading test.
Task 3: Now, arrange your Jelly Babies to test the above
statement, allocating your ‘participants’ according to an
repeated measures design…
Repeated Measures
Participants
Condition 1
Condition 2
A
B
C
D
E
F
G
H
I
J
Concentration on
a reading test.
One the mini-whiteboards,
detail one strength and one
weakness
of
using
a
repeated measures design.
Advantages & Disadvantages
ADVANTAGES:

Fewer participants are required as they take part in all conditions
(i.e. saves time)
DISADVANTAGES:

There may be order effects.

Order effects refer to the order of the conditions having an effect
on the participants’ behaviour. Performance in the second
condition may be better because the participants know what to do.
How might we combat ‘order effects’?
COUNTERBALANCING:

To combat order affects the researcher counter balances the order
of the conditions for the participants. The sample is split in two
groups experimental (A) and control (B). For example, group 1
does ‘A’ then ‘B’, group 2 does ‘B’ then ‘A’ this is to eliminate order
effects – the participants are counter balanced.
Matched Pairs

Pairs of participants are matched from participants in
terms of key variables, such as age and IQ. One
member of each pair is then placed in the
Experimental group and the other member in the
Control group.
Matched Pairs
Participants Participants
Condition 1
One
the
miniwhiteboards, detail
one strength and
one weakness of
using a matched
pairs design.
A
B
C
D
E
A
B
C
D
E
Concentration on
a reading test.
Condition 2
Advantages & Disadvantages
ADVANTAGES:

Reduces participant variables because the researcher
has tried to pair up the participants so that each
condition has people with similar abilities and
characteristics.

Avoids order effects, and so counterbalancing is not
necessary.
DISADVANTAGES:

Very time-consuming trying to find closely matched pairs.

Impossible to match people exactly, unless identical
twins!
Applying Experimental Design
For each of the following studies answer the following
questions :

State the operationalised IV and the DV of the experiment

Name the conditions

State which experimental design has been used

Give one strengths & weakness of that design, specific to the study
1) A psychologist wants to test the theory that doctors have
better spatial awareness than teachers. A group of doctors and
teachers are given a series of spatial awareness tasks (such as
rotating a cube in their heads, giving directions on a map etc.)
which produces a spatial awareness score.
Applying Experimental Design
For each of the following studies answer the following
questions:

State the operationalised IV and the DV of the experiment

Name the conditions

State which experimental design has been used

Give one strengths & weakness of that design, specific to the
study
2) It is proposed that people are more willing to give
money to a male rather than a female charity collector. This
is tested by showing participants photographs of male and
female faces and a description of a fake charity that they
represent. The participants are then asked to say how
much (if any) money they would donate.
Applying Experimental Design
For each of the following studies answer the following questions:

State the operationalised IV and the DV of the experiment

Name the conditions

State which experimental design has been used

Give one strengths & weakness of that design, specific to the study
3) A psychologist wants to test the theory that doctors have
better spatial awareness than teachers. A group of doctors and
teachers are given a series of spatial awareness tasks (such as
rotating a cube in their heads, giving directions on a map etc.)
which produces a spatial awareness score.
Applying Research Methods…
You will now apply everything you have learnt about research
methods to the following studies…
1. Bahrick (1975)
2. Bower (1969)
3. Godden & Baddeley (1975)
4. Loftus & Palmer (1974)
5. Maguire (2000)
6. Peterson & Peterson (1959)
1.
Aim – The research question?
The operationalised IV & DV
Method – Including:
The Design (Laboratory, Field)
Participants (Sample)
What experimental design was
used? Do you think this was the
best choice and why?
Materials required
The procedure
Results – What were the key %s found?
Conclusion – One sentence, summarising the
results, linked to the original aim.
2.
3.
4.
5.
6.
Experiment 1 - Recap
An experimenter wants to see if drug X improves sport
performance. One group are given the drug, another are
given a placebo. Both groups are tested for athletic
ability.

Identify the IV and DV;

Identify the experimental condition and the control
condition.
Experiment 2 - Recap
A researcher is interested in whether alcohol has an
effect on memory. One group of participants are given a
list of words to learn and then given an alcoholic drink.
The other group is given the same list of words, and a
glass of water. The number of words they can remember
is recorded.

Identify the IV and DV;

Identify the experimental condition and the control
condition.
Experiment 3 - Recap
A psychologist is investigating the effect of music on
concentration. A group of participants are given a series
of crossword puzzles to solve, first in a silent room, then
when classical music is played, and then when rock music
is played. The time taken to solve each puzzle is
recorded.

Identify the IV and DV;

Identify the experimental condition and the control
condition.
Experiment 4 - Recap
A scientist has developed a drug which he believes will
increase IQ. He has two groups of participants; one
group he gives the drug to, and the other he gives a
placebo to. After two weeks, he tests their IQ. To try and
avoid any participant variables, he ensures that he has an
equal number of men and women in each group, and
that the participants are of similar ages, intelligence and
social background.

Identify the IV and DV;

Identify the experimental condition and the control
condition.

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