Experimental method

Types of experiment, laboratory and field experiments; natural and quasi-experiments.

What are laboratory experiments? Outline all features

Highly controlled setting where the researcher has control over all the variables in the study.

• The experimenter controls environmental factors, e.g. light and temperature.

• The IV is manipulated/changed by the researcher between the conditions of the experiment. Any effect/change on the DV will be measured.

• All other possible variables that could change the DV are kept consistent between conditions.

What are the advantages of laboratory experiments? A03

• Lab studies are easily replicated due to the use of standardised procedures.

• Due to the high control over the IV and DV and extraneous variables, researcher is more likely to establish cause and effect relationships, so high internal validity.

What are the disadvantages of laboratory experiments? A03

• Lab studies lack mundane realism because they do not reflect the kind of tasks performed in real-world situations, so lower external validity.

• Lab studies can lack ecological validity as the lab setting is artificial. This means that findings from a lab study can not be applied to a range of real-world situations.

• Demand characteristics - Participants may guess the aim of the study and change their behaviour, which affects the validity of the results.

What are field experiments? Outline all features

Experiments conducted in naturalistic settings. For example, in shops, work, school, or anywhere the participants would be expected to behave naturally.

• Independent variable is still manipulated/changed between the conditions of the experiment and then the researcher measures the change in the DV.

• Lack of control over other variables that can change the DV.

• Participants can and can not be aware they are in a field experiment.

What are the advantages of field experiments? A03

• If participants are unaware they are in an experiment, they will not show demand characteristics.

• Tasks used in field experiments are more likely to have mundane realism, so closer to the type of activities that the participant usually carries out.

• Higher ecological validity as they take place in the real-world settings like streets or classrooms - behaviour is more natural and findings are more generalisable to everyday life.

What are the disadvantages of field experiments? A03

• Field studies lack control over possible extraneous variables that could be influencing the measurement of the dependent variable.

• In many field studies, it is difficult or impossible to randomly assign participants to separate conditions, resulting in a change in DV that may be due to participant variables, reducing internal validity.

What are naturalistic experiments? Outline all features

The independent variable have (or will) occurred naturally in the real world without the influence of the researcher. The researcher just records the change in the dependent variables.

• Examples of natural experiments include, the impact of a disaster or political decision on the country, or orphan studies (it is unethical to conduct this in a laboratory experiment).

• Other possible variables that could change the DV cannot be controlled.

What are the advantages of naturalistic experiments? A03

• Natural experiments allow research in areas that could not happen in controlled experimentation, either due to ethical reasons or costs.

• High in external validity because natural experiments are an example of real behaviour occurring in the real world free of demand characteristics.

What are the disadvantages of naturalistic experiments? A03

• As the events have already happened or will happen regardless of the researcher, they have no influence. This means extraneous variables can not be controlled, so the researcher should not claim they found a cause and effect relationship.

• These are often very rare events that can not be replicated exactly to test for reliability.

What are quasi experiments? Outline all features

• Participants can not be randomly assigned between the levels of IV because often the IV in an innate characteristic of the participants. For example, age, gender, education level, ethnicity, mental health status, employment or personality type.

• IV already exists in the participants. The change in the DV will still be measured.

• All other possible variables that could change the DV are kept constant.

Give an example of a Quasi experiment.

For example, A quasi-experiment could compare different income levels (e.g., poor vs. rich) and see how this affects spending behaviour.

What are the advantages of Quasi experiments? A03

• Quasi-experiments are the only way to experimentally study factors that are pre-existing characteristics of participants.

What are the disadvantages of Quasi experiments? A03

The groups may differ in ways other than the IV. Since the IV is a naturally occurring characteristic (like gender or age), other factors linked to that characteristic — such as confidence, ability, or experience — may also vary between groups. These uncontrolled differences can affect the DV, acting as confounding variables and reducing the internal validity of the study.

When reading about an experiment in the exam, what questions should you ask yourself to work out what kind of experiment it is?

1. What is the researcher manipulating or controlling in the study?

• If the researcher is manipulating the independent variable (IV) in a controlled setting = lab

• If the researcher is manipulating the IV, but the setting is a more natural one = field

• If the researcher is not manipulating the DV? = Quasi or naturalistic. Is the IV a characteristic of the participants? = Quasi

2. Where is the study taking place?

• Is the experiment happening in a lab or controlled environment? (Look for words like “controlled,” “artificial setting,” or "in a lab") = lab

• Is the study happening in a real-world environment, such as a school or a workplace? (Look for words like “real-world,” “natural,” or “outside a lab setting”) = field

• Is the researcher studying groups of people in their natural environments without manipulating anything? = naturalistic

3. Do the participants know they are in an experiment?

3. Are the groups created by the researcher or do they already exist?

• If the groups are created by the researcher, such as random assignment of participants to different conditions = more likely lab

• If the groups already exist naturally, like studying the behaviour of males vs. females or comparing older adults to young adults = quasi or natural

5. Did the researcher randomly assign participants to different conditions?