Unit 2 - Experimental design

What do psychologists look to investigate?

Cause-and-effect relationships. They aim to investigate the difference between two conditions, the control condition and the experimental condition. If a significant difference is found in the dependent variable (effect) performance of the control condition and the experimental condition, then we can say the IV (cause) does have an effect.

What are the three main types of experimental design in psychology?

Repeated measures design, independent groups design and matched pairs design.

What is ‘repeated measures design’?

Where participants take part in both the control condition and the experimental condition. Their performance in both is compared; if there is a significant difference, the independent variable has caused an effect on the dependent variable.

What are the strengths and weaknesses of a ‘repeated measures design’?

Strengths are that participant variables are eliminated because their performance is measured against themselves, and that there is a smaller number of participants, making it cost-effective. Weaknesses include that participants are more likely to work out the aim when completing more than one task, resulting in demand characteristics being shown and participants may become practiced or fatigued.

What is ‘independent groups design’?

When participants only take part in one experimental condition. 

What are the strengths and weaknesses of an ‘independent groups design’?

Strengths are that participants are only taking part in one condition so will not become practiced or fatigued. Similarly, participants are less likely to work out the aims and won’t show demand characteristics, however, some weaknesses include that researchers will require more participants, and that participant variables will be present as they are being measured against other people.

What is ‘matched pairs design’?

Where the experimental and control participants are deliberately similar. They match individuals based on a participant variable that could affect performance on the dependent variable.

What are the strengths and weaknesses of a ‘matched pairs design’?

Strengths are that there are no order effects as participants only take part in one condition and that results are less likely to be affected by participant variables than independent groups, however, weaknesses include that twice the number of participants are required compared to a repeated measures design and matching pairs of participants is difficult and costly.

What are the strengths and weaknesses of experimental design associated with?

Order effects, demand characteristics, the number of participants and participant variables.

What are ‘order effects’?

Effects that occur when participating in one condition affects how a participant preforms in another. Participants may become practiced or fatigued. This can be solved by counterbalancing where participants are split into two groups and complete the conditions in the opposite order to cancel out order effects.

What are ‘demand characteristics’?

A type of confounding variable where participants unconsciously work out the aim and act differently, usually through social desirability.

What are ‘participant variables’?

The individual characteristics that all participants have which could affect how they respond to research, e.g. age, gender, personality, intelligence or more.