Experimental Methods

What are the two main ways psychologists investigate human behaviour?

Experimental and Non-experimental.

What is the experimental method psychologists investigate human behaviour?

It involves the manipulation of an independent variable to measure the effect on the dependent variable. Experiments may be laboratory, field, natural or quasi.

What should happen in a ‘true experiment’?

• An independent variable must be manipulated

• There must be elements of random allocation of participants to condition

• All variables must be controlled i.e. kept constant, so we can be confident that the only variable causing any subsequent change on the dependent variable must be the IV (cause and effect)

What is a laboratory experiment? 

An experiment conducted in a highly controlled environment (not always in a lab), the researcher manipulates the IV and records the DV whilst maintaining strict control of extraneous variables - participants are aware they’re taking part but may not always know the true aims of the study.

• Highly controlled environment

• IV manipulated

• High control

• Low realism (artificial setting)

• Risk of demand characteristics

What is a quasi experiment?

Often resembles proper laboratory experiments. However the experiment doesn’t directly manipulate the IV. Also resembles natural experiments but this type of experiment is typically planned whereas natural isn’t.

• Can be done anywhere

• IV isn’t manipulated, since it’s based on pre-existing differences (e.g. gender, age etc.)

• Control depends, often more than natural but less than lab

What is a natural experiment?

When the researcher takes advantage of a pre-existing independent variable, meaning IV isn’t manipulated by the researcher. The IV would have changed even if the experiment wasn’t interested, it’s naturally occurring e.g. flood or earthquake, and the behaviour of the people affected is either compared to their own behaviour beforehand, when possible, or with a control group who haven’t encountered the IV.

• Can be anywhere

• IV occurs naturally

• Very low control

What is a field experiment?

Done in a more natural/everyday setting (anywhere outside a lab) - participants are often unaware they’re participating. The IV is still deliberately manipulated by the researcher 

• In a real world setting e.g. school

• IV manipulated by researcher

• Less control over extraneous variables (compared to lab)

What are the advantages of a laboratory experiment?

• High control over variables → easier to establish cause and effect

• Easy to replicate → increases reliability

• Use of standardised procedures → high internal validity

What are the advantages of a quasi experiment?

• Can compare groups that could not be manipulated for ethical/practical reasons

• Sometimes carried out in controlled settings → some control over extraneous variables

• Useful for studying unique characteristics

What are the advantages of a natural experiment?

• Allows study of real-world issues that can’t be created in a lab (e.g., natural disasters)

• High ecological validity

• Useful when manipulation of IV would be unethical or impossible

What are the advantages of a field experiment?

• Conducted in a natural environment → higher ecological validity

• Participants often unaware they are being studied → less demand characteristics

• Can demonstrate cause and effect while still being realistic

What are the disadvantages of a laboratory experiment?

• Often artificial setting → low ecological validity, participants may behave unnaturally (demand characteristics)

• Can be unethical if deception or stress is used

• Sample often not representative → limited generalisability

What are the disadvantages of a quasi experiment?

• Participants cannot be randomly allocated → confounding variables may affect results

• Cause and effect less certain

• Sometimes limited generalisability (studies focus on specific groups)

What are the disadvantages of a natural experiment?

• No control over IV → can’t establish strong cause and effect

• Difficult to replicate → low reliability

• Extraneous variables can reduce internal validity

What are the disadvantages of a field experiment?

• Less control over extraneous variables → harder to replicate, lower internal validity

• Practical and ethical issues (e.g., consent, invasion of privacy)

• More time-consuming and costly than lab experiments