Specification: Experimental method. Types of experiment: laboratory and field experiments; natural and quasi experiments.

Experimental methods all have one thing in common: they are attempting to find a cause and effect relationship between an independent variable (IV) and dependent variable (DV), and to measure the extent of this effect. There are four different types of experiment:

1. Laboratory experiment

2. Field experiment

3. Natural experiment

4. Quasi experiment

Laboratory experiments

Laboratory experiments are conducted under specified controlled conditions in which the researcher manipulates the independent variable (IV) to measure the effect on the dependent variable (DV). The conditions are heavily controlled in order to minimise the effect of any extraneous variables, to prevent them from becoming a confounding variable which might adversely affect the DV. Participants will be aware that they are taking part in an investigation due to the contrived nature of the situation which may feel unlike real‐life.

Evaluating laboratory experiments

A strength of laboratory experiments is the high degree of control over extraneous variables which can be achieved. A researcher is therefore able, in most cases, to prevent extraneous variables from becoming confounding variables which negatively affect the DV. This provides a high degree of internal validity allowing for conclusions about cause and effect to be drawn between the IV and DV.

A limitation of laboratory experiments is that they can lack external validity. The artificial nature of the environment in which the investigation is taking place means that the study can lack ecological validity. This means that the findings of the study cannot always be generalised to settings beyond the laboratory as the tasks often lack mundane realism and would not be everyday life occurrences. Since participants know they are being investigated their behaviour can also change in an unnatural manner resulting in demand characteristics being seen.

Field experiments

Field experiments are carried out in natural conditions, in which the researcher manipulates the independent variable (IV) to measure the effect on the dependent variable (DV). The ‘field’ is considered any location which is not a laboratory. Participants in a field experiment typically do not know that they are taking part in an investigation with a view to observing more natural behaviour.

Evaluating field experiments

The natural setting means that field experiments often have a higher level of ecological validity, in comparison to laboratory studies. This means that the results are more likely to be representative of behaviour witnessed in everyday life. However, because the setting is more natural, there is less control over extraneous variables. These can then become confounding variables and distort the findings meaning a firm cause and effect relationship cannot be drawn since other factors could have had an impact on the DV, other than the IV.

There are important ethical issues associated with field experiments. Since participants are often unaware that they are in fact participants in a psychological investigation, they cannot give informed consent to take part. As such, the research may involve a breach of their privacy rights and a cost-benefit analysis will need to be conducted before proceeding with any study to ensure the perceived outcomes from the research will outweigh any personal costs to those involved.

Natural experiments

In a natural experiment, the researcher does not manipulate the IV and instead examines the effect of an existing IV on the dependent variable (DV). This IV is naturally occurring, such as a flood or earthquake, and the behaviour of people affected is either compared to their own behaviour beforehand, when possible, or with a control group who have not encountered the IV. It is important to note that it is the IV which is natural in this type of experiment, and not necessarily the context in which the investigation is taking place since participants could be tested in a laboratory as part of the study.

Evaluating natural experiments

The naturally occurring IV means that natural experiments often have a higher level of external validity compared to laboratory and field experiments. These types of investigations are considered high in ecological validity given the real‐life issues that are being studied rather than manipulated artificially. However, natural experiments have no control over the environment and subsequent extraneous variables, which means that it is difficult for the research to accurately assess the effects of the IV on the DV. It may be that a confounding variable has affected the results so a cause and effect relationship must be drawn with extreme caution, if at all.

A strength of using natural experiments is the unique insights gained into real‐life situations from using this methodology. Investigating a naturally occurring IV allows for research to be conducted into areas of psychology that could not be generated for ethical reasons or because of logistical and practical constraints. However, a naturally occurring event that interests researchers may only occur very rarely. This limits the opportunity to generalise the results to other similar events or circumstances.

Quasi experiments

Quasi experiments also contain a naturally occurring independent variable (IV), but one which already exists. However, in this instance the IV is a difference between people such as gender, age or a personality trait. The researcher examines the effect of this IV on the dependent variable (DV). Quasi experiments do not have to be conducted in a natural setting, although they often are. They may also be conducted in a laboratory setting, under controlled conditions.

Evaluating quasi experiments

A limitation of quasi experiments is that participants cannot be randomly allocated to research conditions to remove the issue of bias in the procedure. Since the IV is a naturally occurring difference between the participants, the level of IV to which they belong is predecided. This means the psychologist will be less certain that the IV alone will have caused the effect which is measured through the DV as other dispositional or environmental factors may have played a role in the outcome. That being said, quasi experiments allow researchers to compare different types of people easily to provide insight into similarities or differences between these groups which could not be ethically generated otherwise.

There are methodological issues associated with conducting quasi experiments. When quasi experiments take place under natural conditions, there is no control over the environment and subsequent extraneous variables, making it difficult to be sure that factors such as age, gender or ethnicity have affected the DV. On the other hand, when quasi experiments take place under laboratory conditions the high level of control means that the research often lacks ecological validity, and the findings cannot always be generalised to a real‐life setting since behaviour may not translate outside of the research environment.

Possible exam questions

1. Dr Helpful was interested in studying expectations when meeting a new work colleague for the first time. Each participant who volunteered to take part was taken to the same room where they listened to a description of their new potential work mate called ‘Ms B’. The participants were randomly allocated to one of two groups in the experiment. Dr Helpful gave each participant exactly the same background information about ‘Ms B’, but the order of the information varied depending the experimental condition as follows:

Group 1

Three strengths of Ms B’s CV were followed by three negative comments.

Group 2

Three negative comments about Ms B’s CV were followed by three strengths.

After listening to the excerpt from Ms B’s CV, each participant was asked to state whether they thought Ms B would be a competent colleague to have on their work team or not. Dr Helpful recorded how many participants in each group stated that Ms B was ‘competent’.

Identify which type of experiment was conducted by Dr. helpful. (1 mark)

2. What is meant by the term ‘quasi experiment’? (2 marks)

3. Identify two features of an experiment. (2 marks)

4. Outline what is meant by a laboratory experiment. (2 marks)

5. Identify and explain one difference between a laboratory and a field experiment. (2 marks)

6. A psychologist was interested in investigating whether people with phobias were more aware of their own heartbeat than people who do not suffer with a specific phobia. A matched pairs design was adopted. The sample included eight individuals with a phobia and eight people without a phobia. The investigator asked each participant to make an estimation about how fast their heart was beating (in beats per minute). This figure was compared to their actual heartbeat measurement. Results showed that people with a phobia were more accurate at estimating their own heartbeat than people who did not suffer with a phobia at all.

Explain why this study is considered a quasi experiment. (2 marks)

7. Describe one difference between a natural experiment and a field experiment. (2 marks)

8. Donald, a middle‐aged male politician, approached an adult in a busy street and asked for directions to the nearest bus stop. He repeated this with 14 other adults in the same city.

Each of the 15 adults asked were then approached by a second researcher, called Melania, who showed each of them six photographs of different middle‐aged politicians, including a photograph of Donald. Melania asked the 15 adults to choose the image of the individual who had asked them for directions to the bus stop.

Melania estimated the age of each of the 15 adults and noted whether each participant had chosen the correct photograph of Donald.

Suggest one reason why the researchers decided to use a field experiment rather than a laboratory experiment. (2 marks)

9. What is meant by an extraneous variable? (2 marks)

10. Explain why it is important to control extraneous variables in experimental research. (2 marks)

11. Eleanor was interested in investigating the impact of caffeine on memory.

Discuss advantages of carrying out an experiment like this in a laboratory. (4 marks)

12. Outline and evaluate the use of laboratory experiments in psychological research. Refer to specific examples in your answer. (8 marks)