Experimental Design

When conducting an experiment, psychologists must decide how to assign participants to conditions. This is called the experimental design. The choice of design affects how the results can be interpreted and what conclusions can be drawn. There are three main experimental designs used in psychology.

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The Three Experimental Designs

1. Independent Groups Design

In an independent groups design, different participants are used in each condition of the experiment. Each participant takes part in only one condition.

Example: Testing whether background music affects memory:

• Group A (condition 1): learns a word list in silence
• Group B (condition 2): learns a word list with background music
• Different people in each group

Advantage	Disadvantage
No order effects (boredom, fatigue, practice) because each participant only does one condition	Participant variables — differences between people in each group may affect results (e.g. one group might have naturally better memories)
Participants are less likely to guess the aim of the study	Requires more participants (twice as many as repeated measures)