Designing Experiments

Question 1

Experimental Methods

Answer 1

Experimental methods are the most rigorous way of testing hypotheses because they seek to establish cause and effect.

Question 2

Experiment

Answer 2

Most rigorous test. Establishes cause and effect. 3 key features: manipulation of IV, randomisation and control.

Question 3

What are the 4 types of experiments?

Answer 3

1. Laboratory
2. Quasi
3. Field
4. Natural

Question 4

Laboratory

Answer 4

Meets all 3 key features.

Question 5

Quasi

Answer 5

No randomisation. Participants allocated to conditions according to characteristics they already possess.

Question 6

Field

Answer 6

Control of IVs but not EVs. Not necessarily random allocation.

Question 7

Natural

Answer 7

None of the 3 key features.

Question 8

Advantages of Laboratory Experiments

Answer 8

• High level of control over IVs an EVs.
• Replicability.
• Can establish cause and effect.

Question 9

Disadvantages of Laboratory Experiments

Answer 9

• Lacks ecological validity.
• Investigator effects.
• Demand characteristics.
• Artificiality.

Question 10

Advantages of Quasi Experiments

Answer 10

• High ecological validity.

Question 11

Disadvantages of Quasi Experiments

Answer 11

• Lack of control.
• Not replicable.

Question 12

Advantages of Field Experiments

Answer 12

• High levels of ecological validity.
• Less demand characteristics.
• Can establish cause and effect.

Question 13

Disadvantages of Field Experiments

Answer 13

• Less control over EVs.
• More time consuming.
• Random allocation difficult.

Question 14

Advantages of Natural Experiments

Answer 14

• High levels of ecological validity.
• Useful where it would be unethical or impossible to manipulate the IV.

Question 15

Disadvantage of Natural Experiments

Answer 15

• Loss of control over EVs; cannot establish cause and effect.
• No random allocation of participants to conditions.

Question 16

A true experiment has three key features:

Answer 16

1) Manipulation of the IV to produce a change in the DV.
2) Random allocation of participants to the different conditions.
3) Control of all the EVs so they remain constant.

Question 17

The three features of true experiments are met to different degrees by different types of experiments:

Answer 17

1) Lab experiments (meets all three features).
2) Quasi-experiment (manipulation of IV and control of extraneous variables but not randomisation. Participants are allocated to conditions according to characteristics that they already possess).
3) Field experiment (controls of the IV but not the EVs, not necessarily random allocation).
4) Natural experiment (no manipulation of IV or EVs, not random allocation.

Question 18

Experimental Design

Answer 18

In any basic experiment, there are two conditions; the experimental condition and the control condition.
Control condition is the condition where participants receive no experimental treatment. The group of participants who do not receive any experimental treatment are the control group and they act as a comparison to participants who do. A decision has to be taken as to whether participants will participate in one or both conditions. This will determine the experimental design.

Question 19

Three basic experimental designs:

Answer 19

1) Independent groups design.
2) Repeated measures design.
3) Matched pairs design.

Question 20

Independent groups design

Answer 20

Each participant takes part in one condition only. Participants are divided strictly on random basis. Should not be used unless there is some reason why repeated measures cannot be used.

Question 21

Advantages of independent groups design

Answer 21

• Addresses order effects.
• Reduces demand characteristics.
• Can use the same stimulus.

Question 22

Disadvantages of independent groups design

Answer 22

• Individual differences.
• Less effective at controlling participant variables.
• More participants needed.

Question 23

Repeated measures design

Answer 23

All participants perform under both conditions of the experiment. This introduces a confounding variable; order effect. To prevent it, counterbalancing; half of participants perform condition 1 before condition 2 and the other half perform condition 2 before condition 1.

Question 24

Advantages of repeated measures design

Answer 24

• Prevents individual differences.
• Fewer participants needed.

Question 25

Disadvantages of repeated measures design

Answer 25

- Order effects. - Demand characteristics. - Can't use the same stimulus.

Question 26

Matched pairs design

Answer 26

Imitates repeated measures design but without each participant performing under both conditions. Participants are matched on all relevant variables, that is all variables that may affect the DV. Difficult to decide which variables are relevant. Ideally identical twins raised together.

Question 27

Advantages of matched pairs design

Answer 27

- Prevents individual differences. - Addresses order effects.

Question 28

Disadvantages of matched pairs design

Answer 28

- Difficult to obtain/match - impractical. - More participants needed.