Experimental Design

Question 1

What is an experimental design?

Answer 1

• If an IV has more than 1 level, the researcher has to decide who’ll take part in each condition
• So an experimental design is how participants are used in experiments (what conditions they’re assigned to) and set of conditions used to control influences (e.g. participant variables)

Question 2

What are order effects?

Answer 2

An extraneous variable arising from the order in which conditions are presented e.g. practice effect or fatigue effect

Question 3

What are the 3 types of experiment design?

Answer 3

• Repeated measures
• Independent measures
• Matched pairs

Question 4

What is a repeated measures design?

Answer 4

• All participants receive all levels of the IV, e.g., each participant does a memory test with the TV. Then a week later, each do a similar test without the TV on
• We then compare the performance

Question 5

What are disadvantages of repeated measures design?

Answer 5

• Participant have to endure all conditions of the IV and the order in which these tasks are completed may have an impact (order effects)
• Participants may be more likely to work out the aim of study when they experience all conditions, which means there’s more chance of demand characteristics

Question 6

What are methods of dealing with order effects?

Answer 6

• Using counterbalancing involves alternating the order in which participants perform in different conditions of an experiment
• e.g. a group performs AB and another does BA, or all participants take part in each condition twice

Question 7

What is an advantage of repeated measures design?

Answer 7

The same participants take part in all conditions and their performance in one condition is compared with their own performance in another, means there’s no issues with participant variables

Question 8

What is an independent groups design?

Answer 8

• Participants are placed in separate groups. Each group does one level of the IV e.g. A does the task with the TV on, B does the task with no TV
• We compare the performance of the two groups

Question 9

What are disadvantages of independent groups design?

Answer 9

• The participants who occupy each condition aren’t the same. So, if a difference in the DV was found, it’s more difficult to know if the change is a result of the IV and not that participants variables
• Participants take part in only one condition which means twice as many participants are needed to produce the same amount of data

Question 10

What are methods of the dealing with participant variables?

Answer 10

Randomly allocate participants to conditions which should distribute participant variables evenly. Random allocations can be done by putting participants name in a hat and drawing out names.

Question 11

What is an advantage of independent groups design?

Answer 11

Avoids order effects (practice/fatigue), participants don’t have the opportunity to practice and are less likely to becomes tired or bored

Question 12

What is a matched pairs design?

Answer 12

• A compromise is to use 2 groups of participants but match participants on key characteristics believed to affect the DV (e.g. IQ)
• Then one member of the pair is randomly allocated to group A and the other to group B. The procedure is the same as an independent design

Question 13

What are advantages of a matched pairs design?

Answer 13

• As participants take part in only one condition, it reduces order effects and demand characteristics
• Attempts to reduce participants variables by matched participants

Question 14

What are disadvantages of a matched pairs design?

Answer 14

• It’s impossible to control all participants variables are you can only match on known relevant variables
• Matching participants is a time-consuming and difficult process

Question 15

How would limitations of matched pairs design be overcome?

Answer 15

• Restrict the number of variables to match to make process easier
• Conduct a pilot study to consider key variables that might be important when matching