Experimental Design Flashcards
(15 cards)
What is repeated measures design?
The same participants are used
in all conditions of the
independent variable.
What are the advantages of repeated measures design?
Individual differences are eliminated
therefore any difference between their
performance in each level of the IV
should be to the experimenter’s
manipulation.
• Fewer participants required.
What are the disadvantages of repeated measures design?
Order effects such as practice, boredom or
fatigue may occur, although these can be
evenly distributed across conditions by
counterbalancing.
• Demand characteristics: because
participants take part in all conditions.
• It is sometimes not possible to use the same
material in each condition.
What is independent groups design ?
Participants placed in separate groups. Each group
does one level of the
independent variable.
What are the advantages of independent groups?
No order effects: participants are only
involved in one condition.
• There is less opportunity to become
aware of the aim reducing demand
characteristics.
• The same material can be used in all
conditions
What are the disadvantages of independent groups?
Participant variables are introduced.
Differences between the conditions may be
caused by the different people rather than
the independent variable.
• More participants are required.
What is matched pairs design?
Pairs of participants are closely
matched on a relevant
characteristic (e.g. age, gender,
etc.). Each participant in the pair
is randomly allocated to one
condition or the other.
What are the advantages of Matched pairs.?
Avoids order effects.
• Avoids demand characteristics.
• Reduces individual differences.
• The same material can be used in both
conditions.
What is the disadvantage of matched pairs?
It is difficult to match everything about the
participants.
• It is very time consuming and requires more
participants
What is random allocation?
allocating participants to experimental groups in an unbiased way, so they have
an equal chance of being selected to take part in each condition. This is to evenly distribute
participant characteristics across the conditions to avoid extraneous variables and improves
internal validity. It is used to address the problem of participant variables (individual
differences) in an independent groups design. This can be done by assigning each participant
a number or identifying them by name; the names or numbers are placed in a random
number generator/hat; the first participant drawn is assigned to condition 1, the second to
condition 2 OR the first 15 participants are assigned to condition 1 and the next 15 are
assigned to condition 2.
What is counter balancing?
used to control for the impact of order effects in repeated measures
design and improve internal validity. It involves making sure each condition comes first or
second in equal amounts. E.g. Half the participants take part in condition A then B, and the
other half take part in condition B then A. Counterbalancing ensures order effects are
distributed evenly across all conditions. Counterbalancing does not reduce order effects
because all participants still take part in all conditions therefore order effects are still present,
but their effect is balanced across the conditions.
What is randomisation?
the use of chance wherever possible when designing materials and
deciding the order of conditions. This is to avoid researcher biasinfluencing the design of the
study; it is an attempt to control investigator effects and improve internal validity. E.g. if in
a memory experiment the participants have to learn a list of words; the order of the words
should be randomly generated. Or if the experiment involves a number of conditions, the
order of these conditions should be randomly determined.
What is standardisation?
ensuring all participants have exactly the same environment,
information and experience, so individual experience does not confound the results, thus
improving internal validity. Standardised procedures ensure all participants are tested
under the same conditions to enable to deal with experimenter bias and facilitate
replication to ensure findings can be checked for reliability. Standardised procedures should
include a set of standardised instructions that are given in the same way to all participants
to deal with investigator effects
How do you Improve the reliability of experiments?
When possible, it is better to take more than one measurement from each participant and
take a mean score. This reduces the impact of any anomalous score. Pilot studies can be
used to check the proposed method measurements works properly and that participants can
use any apparatus successfully.
How do you improve external validity in experiments?
Ecological Validity can be improved by conducting the experiment in a more naturalistic, real
life setting e.g. a field experiment. Population validity can be improved by taking larger, more
varied samples, for example including a wider age group or geographical area.
