Subjects Design Flashcards
What is Subjects Design?
The assignment of participants to experimental conditions (levels of the IV)
What are the 3 types of Subjects Design?
1) Between-subjects / Independent groups
2) Within-subjects / Repeated measures
3) Mixed-designs: Mixture of between and within
What is a Between-subjects design?
- There are 2 groups of different Ps
- Ps go through ONLY 1 level of the IV (different participants are used for each of the conditions)
What is a Within-subjects design?
- There is ONLY 1 group of Ps
- Ps go through 2 levels of the IV (repeated measures; same participants are used for both conditions)
What is the issue with the Within-subjects design?
Order Effects
- Participants get bored, tired or lose focus/attention when performing a task for the 2nd time
What is the issue with the Between-subjects design?
Participants in Group 1 and Group 2 may not have equal characteristics which may affect the result/induce bias
e.g. Group 1 majority may not like music but Group 2 majority do. So in a study investigating the effects of music on studying, Group 1 may perform worse
How do we ensure that any differences between the 2 groups in the Between-Subjects design are minimised?
(e.g. differences in age, tiredness, interest)
Random Allocation
What is Random Allocation?
Ensures that each participant is equally likely to be assigned to any IV level
Why do we randomly allocate participants to the conditions in a Between-Subjects design?
1) Randomising distributes the occurrence of potential moderating variables equally among experimental conditions (make it fairer)
2) Prevents experimenters (un)intentionally biasing their results
3) Enables the use of powerful statistical tests that can help determine causal relationships between variables
How do we minimise order effects following a Within-Subjects design?
Counterbalancing
What is Counterbalancing following a Within-Subjects design?
Split the group of participants in half (A and B)
- Group A can participate in Task 1 then Task 2
- Group B can participate in Task 2 then Task 1
Order effects will still influence Ps performance, but the effect of that influence will be evenly spread across each level of the IV
What are Factorial designs?
Experimental designs with 2 or more IVs
What design should we use if the experiment has 2 IVs or more IVs?
Factorial design
What do Factorial Designs allow us to do/ask?
1) What effect does IV 1 have on the DV?
2) What effect does IV 2 have on the DV?
3) What effect does the interaction of IV 1 and IV 2 have on the DV?
e.g. = Effects of alcohol consumption and work shift patterns on work productivity
DV: work output
IV 1: shift pattern
IV 2: alcohol consumption
What design is used when a study has 2 IVs and 4 groups, each group undergoing 1 condition?
Fully Independent Factorial Design (between subjects)
What design does this experiment follow?
Effects of alcohol consumption (IV1) and work shift patterns (IV2) on work productivity (DV)
DV = work output (productivity)
IV 1 = Time of day – between-subjects
(Randomly assign Ps to either the dayshift or nightshift group)
IV 2: Alcohol consumption – between-subjects
(Randomly assign Ps to either take the test with alcohol or without alcohol)
Fully Independent Factorial Design (between subjects)
How many groups does an experiment following a Fully Independent Factorial Design (between subjects) have?
4 groups (2 groups for IV 1 and 2 groups for IV 2)