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

What are the Types of Experiment?

• Laboratory experiment.
• Field experiment.
• Natural experiment.
• Quasi experiment.

What is an Experiment?

• Research method where researcher manipulates an IV and measures effect on a DV.

• Main aim is to establish cause and effect.

What is an Independent Variable (IV)?

• Variable manipulated or changed by the researcher.

What is a Dependent Variable (DV)?

• Variable measured by the researcher.

What is Operationalisation?

• Clearly defining variables so they can be measured objectively.

Why is Operationalisation Important?

• Makes variables measurable.
• Improves reliability because procedures can be replicated consistently.

Example of Operationalisation

• Aggression operationalised as number of punches thrown in 10 minutes.
• Intelligence operationalised as IQ score out of 100.

Why are Experiments able to establish Cause and Effect?

• Researcher manipulates IV.
• Researcher measures DV.
• Extraneous variables can be controlled.

What is a Laboratory Experiment?

• Experiment conducted in highly controlled artificial environment where researcher manipulates IV.

Example of a Laboratory Experiment

• Participants drink caffeine in lab before completing memory test.
• IV = amount of caffeine.
• DV = memory score.

Strengths of Laboratory Experiments

• High control over extraneous variables improves internal validity.
• Standardised procedures make studies easier to replicate increasing reliability.

Why do Laboratory Experiments have High Internal Validity?

• Researchers can control extraneous variables.
• Makes it more likely IV caused changes in DV.

Limitations of Laboratory Experiments

• Artificial setting may reduce ecological validity.
• Participants may show demand characteristics.

Why do Laboratory Experiments often have Low Ecological Validity?

• Artificial environments may not reflect real life behaviour.

What are Demand Characteristics?

• Participants guess aims of study and alter behaviour.

What are Investigator Effects?

• Researcher behaviour unintentionally influences participants.

What is a Field Experiment?

• Experiment where IV is manipulated in natural real-world setting.

Example of a Field Experiment

• Researchers change supermarket music and measure customer spending.
• IV = type of music.
• DV = amount spent.

Strengths of Field Experiments

• Higher ecological validity because behaviour is more natural.
• Reduced demand characteristics because participants may not know they are being studied.

Why do Field Experiments usually have Higher Ecological Validity?

• Behaviour occurs in more realistic natural settings.

Limitations of Field Experiments

• Less control over extraneous variables reducing internal validity.
• Difficult to replicate because natural environments constantly change.

Why do Field Experiments have Lower Reliability?

• Natural settings are difficult to standardise and replicate consistently.

Ethical Issue with Field Experiments

• Participants may not provide informed consent because they are unaware they are being studied.

What is a Natural Experiment?

• Experiment where IV naturally occurs and is not manipulated by researcher.

Example of a Natural Experiment

• Comparing people affected by flood with those not affected.
• Flood acts as IV.

Strengths of Natural Experiments

• Useful when variables cannot be ethically manipulated.
• Often have high ecological validity because situations are naturally occurring.

Why are Natural Experiments useful in Psychology?

• Some variables such as trauma or disasters cannot ethically be manipulated by researchers.

Limitations of Natural Experiments

• Very little control over extraneous variables.
• Difficult to establish cause and effect confidently.

Why is Cause and Effect harder to establish in Natural Experiments?

• Extraneous variables may influence DV.
• Participants cannot usually be randomly allocated.

What is a Quasi Experiment?

• Experiment where IV is based on pre-existing participant differences.

Example of a Quasi Experiment

• Comparing aggression levels in males and females.
• Gender acts as IV.

Strengths of Quasi Experiments

• Useful when participant variables cannot be manipulated.
• Often involve naturally occurring behaviours increasing realism.

Limitations of Quasi Experiments

• Participants cannot be randomly allocated to conditions.
• Less control over participant variables reduces internal validity.

Difference between Natural and Quasi Experiments

• Natural experiments use naturally occurring events/situations as IV.
• Quasi experiments use pre-existing participant characteristics as IV.

Examples of Naturally Occurring Events in Natural Experiments

• Floods.
• Pandemics.
• School changes.
• Natural disasters.

Examples of Pre-existing Participant Characteristics in Quasi Experiments

• Gender.
• Age.
• Autism diagnosis.

What is an Extraneous Variable?

• Any variable other than IV that could affect DV.

Example of an Extraneous Variable

• Noise distracting participants during memory test.

Why are Extraneous Variables a Problem?

• May influence DV and reduce validity of findings.

What is a Confounding Variable?

• Uncontrolled extraneous variable that actually affects DV.

Why are Confounding Variables a Serious Problem?

• Makes it unclear whether IV caused changes in DV.

How do Researchers establish Control in Experiments?

• Standardised instructions.
• Same environment for participants.
• Random allocation.

What is Random Allocation?

• Randomly assigning participants to experimental conditions.

Why is Random Allocation Important?

• Reduces participant variables.
• Improves internal validity.

Example of Random Allocation

• Participants assigned to groups using names drawn from hat.

What is Standardisation?

• Keeping procedures identical for all participants.

Why is Standardisation Important?

• Improves reliability because study can be replicated consistently.

Difference between Laboratory and Field Experiments

• Laboratory experiments occur in controlled artificial settings.
• Field experiments occur in natural settings with less control.

Which Type of Experiment has Highest Control?

• Laboratory experiments because extraneous variables can be controlled more effectively.

Which Type of Experiment usually has Highest Ecological Validity?

• Field and natural experiments because behaviour occurs in realistic settings.

Which Type of Experiment is easiest to Replicate?

• Laboratory experiments due to standardised controlled procedures.

Difference between Experiments and Correlations

• Experiments manipulate IV and establish cause and effect.
• Correlations measure co-variables and cannot establish causation.