Term
Experimental Design
What is experimental design?
Answer
Definition
It is how participants are allocated to conditions and how variables are manipulated and controlled in an experiment.
In repeated measures design, the same participants take part in all conditions of the experiment. For example, measuring the reaction time of a group of participants both when sleep-deprived and fully rested.
Controls for participant variables because each participant acts as their own control, improving reliability.
Requires fewer participants, which is cost-effective and time-efficient.
Greater statistical power because individual differences are eliminated from comparison.
Prone to order effects such as fatigue (getting tired by the second condition) or practice (improvements due to familiarity with the task).
Sometimes not practical if the manipulation has lasting effects that cannot be undone (carryover effects).
Demand characteristics might be more pronounced because participants experience all conditions and may guess the aims.
In this design, different participants are used in each condition. One group might be tested under the sleep-deprived condition, another under the rested condition.
No order effects or practice effects because participants are tested only once.
Often quicker per participant because each completes only one condition.
More participants are needed, increasing time and cost.
Participant variables are not controlled naturally, potentially increasing variability. Random allocation helps to minimize these differences but cannot eliminate them entirely.
Participants are matched on key variables (e.g., age, IQ) and then split into conditions; pairs or groups are equivalent based on these variables. For example, pairing two participants with similar IQ scores and assigning one to the sleep-deprived group and the other to the control group.
Controls for participant variables better than independent measures design.
Avoids order effects since each participant takes part in only one condition.
Time-consuming and difficult to find suitable matches on all relevant variables.
Matching may be incomplete, leaving some differences uncontrolled.
More complex logistics and analysis.
Counterbalancing is a method used to reduce order effects by changing the order in which participants complete conditions.
Prone to order effects such as fatigue or practice.
Design Choice: Researchers choose designs based on the nature of the study, the variables under investigation, ethical considerations, and practical constraints.
What is experimental design?
It is how participants are allocated to conditions and how variables are manipulated and controlled in an experiment.
Name the three main types of experimental designs.
Repeated measures, independent measures, and matched participants.
What is a repeated measures design?
The same participants take part in all conditions of the experiment.
Name one strength of repeated measures design.
Controls for participant variables by having participants act as their own controls.
What are order effects?
Fatigue or practice effects that occur when participants experience multiple conditions in sequence.
What is counterbalancing?
A method to reduce order effects by changing the order of conditions for participants.
What characterizes independent measures design?
Different participants are used in each condition.
Give one strength of independent measures design.
No order or practice effects since participants complete only one condition.
What is a key weakness of independent measures design?
Participant variables are not naturally controlled, which may increase variability.
Describe the matched participants design.
Participants are matched on key variables and split into conditions based on these matches.
What is a benefit of matched participants design over independent measures?
Better control over participant variables without order effects.
What is a limitation of matched participants design?
It is time-consuming and difficult to find perfect matches.
Why do researchers choose different experimental designs?
Based on the study’s nature, variables, ethics, and practical constraints.