Experiments: types & designs

Lab experiment

• Highly controlled environment

• Standardized procedures

• Researcher manipulates IV & measures DV

• Participants know they’re taking part

Strength AO3

• P - high level of control over extraneous variables (eg distractions & lighting)

• E - this means researchers can isolate the IV and be more confident that changes in the DV are due to the IV rather than other factors.

• T - increases the internal validity of the findings.

Limitation AO3

• P - lack ecological validity.

• E - the artificial setting may cause participants to behave differently than they would in real life. Also usually uses artificial, trivial tasks that lack meaning & aren’t reflective of everyday tasks

• T - findings may not generalise to real-world behaviour

• P - demand characteristics

• E - participants may guess the aim of the study and alter their responses accordingly to how they think the experimenter wants them to act
  T - reduces the validity of the results.

Field experiment

• Natural setting

• Researcher manipulates IV & measures DV

• Participants usually don’t know that they’re taking part

Strength AO3

• P - high ecological validity.

• E - behaviour is studied in a natural environment where participants act more realistically. No demand characteristics

• T - findings are more generalisable to real-life situations

Limitation AO3

• P - less control over extraneous variables in field experiments.

• E - many uncontrolled variables in real-world settings may become confounding variables & influence behaviour

• T - reduces internal validity & can’t establish clear C&E relationship

• P - raise ethical concerns.

• E - participants are often unaware they are being studied, so informed consent cannot be obtained

• T - this breaches the ethical guideline of informed consent

Natural experiment

• Lab setting or natural setting

• IV is naturally occurring

• Participants may or may not know that they’re taking part

Strength AO3

• P - allow researchers to study variables that would be unethical or impractical to manipulate

• E - for example, studying the effects of real-life events like brain injury

• T - increases the applicability of research to real-world issues

Limitation AO3

• P - little control over extraneous variables.

• E - since the IV occurs naturally, many other factors may influence the DV.

• T - difficult to establish cause and effect.

• P - depend on naturally occurring events.

• E - these events may be rare and unpredictable

• T - research may be difficult to replicate

Quasi experiment

• Lab setting or natural setting

• IV is based on pre-existing differences (eg gender)

• Participants may or may not know that they’re taking part

Strength AO3

• P - more ethical than lab experiments.
  E - the IV is based on pre-existing differences, so no manipulation is required.

• T - avoids ethical issues associated with assigning participants to conditions.

Limitation AO3

• P - difficult to establish cause and effect.

• E - other variables may influence the DV such as individual differences

• T - conclusions about causation are less reliable

Independent measures

• Participants take part in one condition only

Strength AO3

• P - minimizes order effects

• E - participants only take part once, so practice or fatigue cannot influence performance

• T - increases the validity of the results

Limitation AO3

• P - affected by participant variables

• E - individual differences may effect the results (eg intelligence & personality)

• T - reduces internal validity because changes in the DV may not be due to the IV. Harder to establish a C&E relationship

Repeated measures

• Same participants take part in both conditions

Strength AO3

• P - minimises individual differences

• E - the same participants are used in all conditions, so individual differences are constant

• T - increases internal validity

• P - fewer participants are required

• E - the same group is reused across conditions

• T - this makes the study more efficient and economical

Limitation AO3

• P - affected by order effects.

• E - participants may improve through practice or perform worse due to fatigue

• T - reduces internal validity

Matched pairs design

• Participants are matched in pairs based on relevant characteristics, and one from each pair is placed in each condition.

Strength AO3

• P - reduces individual differences
  E - participants are matched on key characteristics before allocation.
  T - increases internal validity compared to independent measures

Limitation AO3

• P - matching participants can be difficult and time-consuming.

• E - may be hard to find participants with similar characteristics & time consuming matching them

• T - not the most time effective or cost efficient method

• P - matching is never completely accurate

• E - participants may still differ in ways not controlled for.

• T - some participant variables may still affect results, reducing validity.