Psychology - Experimental Design

Notes from my textbook for my own learning, that i'm sharing with you.

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Reianna Shakil L6EF Psychology
Experimental Design
Experimental design: A set of procedures used to control the influence of factors
such as participant variables in an experiment.
Independent groups: Participants are allocated to two (or more) groups
representing different experimental conditions. Allocation is usually done using
random techniques.
Matched pairs: Pairs of participants are matched in terms of key variables such as
age and IQ. One member of each pair is placed in the experimental group and the
other member in the control group.
Repeated measures: Each participant takes part in every condition under test.
Counterbalancing: An experimental technique used to overcome order effects.
Counterbalancing ensures that each condition is tested first or second in equal
Order effect: In a repeated measures design, an extraneous variable arising from
the order in which conditions are presented, e.g. a practice effect or fatigue effect.
Baddeley's study of short-term memory encoding
Baddeley's experiment used an independent groups design.
Each participant was tested in only one condition.
There were 4 separate (independent) groups of participants (groups A, B, C, D).
We could redesign this as a repeated groups design.
Each participant would then be tested on all four conditions: lists A, B, C, D.
Matched pairs design
This is a 3rd kind of experimental design. Involves the use of 2 different groups of
participants; each participant in Group A is paired with one in Group B. This is done by
pairing participants on key variables (e.g. IQ, memory ability, gender) and then placing
1 member of each pair in each group. The characteristics for matching must be
relevant to the study - i.e. you wouldn't match participants on gender if you were
testing memory, unless there was some evidence to suggest otherwise.
Counterbalancing ensures that each condition is tested first or second in equal
amounts. If participants do the same memory test twice in a day ­ morning and then
afternoon, it is expected that performance will improve with practice, but they might
do worse because they are bored with the task. These are called order effects which
can be dealt with using counterbalancing. There are two ways to counterbalance
order effects. In each case, we have two conditions:
Condition A ­ test done in the morning
Condition B ­ test done in the afternoon

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Reianna Shakil L6EF Psychology
Way 1: AB or BA
Divide participants into two groups:
Group 1 - each participant does A then B
Group 2 ­ each participant does B then A
Note that this is still a repeated measures design even though there are two groups
of participants, because comparison will be made for each participant on their
performance on the two conditions (morning and afternoon).
Way 2: ABBA
This time, all participants take part in each condition twice.…read more


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