EXPERIMENTAL DESIGNS

What is a design

How participants are organised in conditions

How many experimental designs are there

3

What are the 3 experimental designs

Independent groups, repeated measures, matched pairs

What is an independent group

Where there is different people in each condition, e.g, 20 participants doing a memory test while drinking coffee vs 20 participants doing the test with no coffee

What is a strength of independent groups

The design of independet groups avoids order effects

Each participant only takes place in one condition

This prevents fatigue or practice effects, increasing internal validity

What is a weakness of independent groups

Participant variables can affect results

Different people are used in each condition, so natural differences such as memory ability may influence results

This reduces internal validity and makes it harder to attribute changes in the dependent variable to the independent variable

What are repeated measures

The same participants are in all conditions, e.g. 20 participants do memory test while drinking coffee, and the same participants do memory test without coffee

What is a strength of repeated measures

It eliminates participant variables

The same participants take part in all conditions

This ensures that all differences between conditions are due to the independent variable, improving internal validity

What is a weakness of repeated measures

Order effects can impact results

Parricipants may improve due to practice, or perform worse due to fatigue

This threatens internal validity unless counterbalancing is used to minimise these effects

What are matched pairs

Taking different participants for each condition, but matching them on key variables that matter for the study, e.g. in a group of 40 people, each person is paired with another who has similar age, memory ability and caffeine tolerance. After being paired, person A gets put into the condition of drinking coffee during the memory test whereas person B gets allocated no to drink coffee

What is a strength of matched pairs

They reduce order effects and participant variables

Participants only take place part in one condition but are matched on relevant variables

This makes the design less practical and may not eliminate all participant differences

What is a weakness of matched pairs

Matching participants is time consuming and difficult

It requires pre testing and careful pairing

This makes the design less practical and may not eliminate all participant differences