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Experiments in Psychology

Experimental Research Outline

An experiment is a research method used in psychology to investigate cause-and-effect relationships by manipulating an independent variable (IV) and measuring its effect on a dependent variable (DV). Experiments allow researchers to draw conclusions about causal relationships through control and manipulation of variables. There are three key types:

1

Laboratory Experiments

Highly controlled, artificial environment.
2

Field Experiments

Natural environment, IV still manipulated.
3

Quasi Experiments

IV is a pre-existing characteristic (not manipulated).

Key Features of Experimental Design

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IV (Independent Variable)

The variable that the researcher manipulates to investigate its effect.
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DV (Dependent Variable)

The variable measured to see if it changes due to the manipulation of the IV.
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Control Variables

Variables kept constant to prevent them from influencing the DV.
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Random Assignment

Allocating participants to conditions in a way that each has an equal chance of being in any condition; mainly applies to laboratory experiments and helps reduce participant bias.

Laboratory Experiments: Control vs Reality

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Strengths
  • High control of extraneous variables: By controlling the environment, researchers can minimize confounding variables, increasing internal validity and confidence that changes in DV are caused by the IV.
  • Replicability: Due to the standardized and controlled procedures, lab experiments can be easily replicated to check reliability and consistency of results.
  • Precise measurement: Lab settings often allow for the use of specialised equipment, making data collection accurate and objective.
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Weaknesses
  • Low ecological validity: Because lab settings are artificial, the behaviours observed may not reflect real-life behaviours; participants might respond differently than they would in a natural context.
  • Demand characteristics: Participants may guess the aims of the study and alter their behaviour accordingly, reducing the authenticity of their responses.
  • Ethical constraints: Some manipulations may not be feasible in laboratory settings if they cause distress.

Field Experiments: Validity vs Control

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Strengths
  • Higher ecological validity: Studying behaviour in a natural setting means findings are more likely to generalize to real-world situations.
  • Reduced demand characteristics: Participants may be less aware of being observed or part of a study, minimizing demand effects.
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Weaknesses
  • Less control over extraneous variables: Natural settings introduce variables that cannot be fully controlled, potentially confounding results and reducing internal validity.
  • Practical and ethical difficulties: Manipulating variables in the real world can sometimes be impractical or raise ethical concerns, especially if participants cannot give informed consent.
  • Replicability issues: Due to the less controlled environment, it can be harder to replicate field experiments exactly.

Quasi Experiments: Natural Differences

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Strengths
  • Practicality: Quasi experiments allow study of variables that cannot be manipulated ethically or practically, e.g., the impact of brain damage on memory.
  • Application to ‘real’ differences: They reflect naturally occurring variables, making results highly relevant to real-life populations.
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Weaknesses
  • No random allocation: Since participants are grouped based on pre-existing variables, there is no random assignment, increasing the risk of participant variables acting as confounds.
  • Lower internal validity: Because the researcher does not manipulate the IV, causal conclusions are tentative; extraneous variables may influence results.
  • Less control: Similar to field experiments, less control over extraneous variables can affect validity.

Comparison and Application Summary

When to use which design

  • Laboratory experiments are the best choice when control and replicability are priorities.
  • Field experiments offer a balance between control and ecological validity, suited to studying behaviour in natural settings but with some experimental manipulation.
  • Quasi experiments provide insights where manipulation is impossible or unethical, allowing study of natural differences but with limitations on causal inferences.

Key Experimental Examples

Understanding the application of experimental types through classic psychological research:

LAB

Milgram’s Obedience Study

Milgram’s obedience study was a laboratory experiment, manipulating proximity and pressure to obey authority and measuring obedience levels.
FIELD

Piliavin’s Subway Study

Piliavin’s subway study was a field experiment observing helping behaviour in a realistic public setting.
QUASI

Sperry's Split-Brain Research

Sperry's split-brain research is a quasi experiment examining naturally occurring brain lesions to study lateralisation.

Ethical Considerations Specific to Experiments

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Core Requirements: In laboratory and field experiments, participants should provide informed consent, though in some field experiments, covert observation may challenge this. Deception must be justified and followed by debriefing. Researchers must avoid harm and respect participants’ rights.

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Experiments in Psychology
Term
Experiment in Psychology

What is an experiment in psychology?

Answer
Definition

A method to investigate cause-and-effect by manipulating an IV and measuring its effect on a DV.

Term
Independent Variable (IV)

What is the Independent Variable (IV)?

Answer
Definition

The variable that the researcher manipulates.

Term
Dependent Variable (DV)

What is the Dependent Variable (DV)?

Answer
Definition

The variable measured to see if it changes due to the IV.

Term
Laboratory Experiments

What are laboratory experiments?

Answer
Definition

Experiments conducted in a controlled, artificial environment.

Term
Strength of Laboratory Experiments

What is a key strength of laboratory experiments?

Answer
Strength

High control of extraneous variables leading to increased internal validity.

Term
Weakness of Laboratory Experiments

What is a main weakness of laboratory experiments?

Answer
Weakness

Low ecological validity due to artificial settings.

Term
Field Experiments

What are field experiments?

Answer
Definition

Experiments conducted in natural settings where the IV is still manipulated.

Term
Advantage of Field Experiments

What advantage do field experiments have over laboratory experiments?

Answer
Advantage

Higher ecological validity.

Term
Quasi Experiment

What is a quasi experiment?

Answer
Definition

An experiment where the IV is a pre-existing variable, not manipulated by the researcher.

Term
Internal Validity in Quasi Experiments

Why do quasi experiments have lower internal validity?

Answer
Reason

Because there is no random allocation and the IV is not manipulated.

Term
Random Assignment

What is random assignment?

Answer
Definition

Allocating participants to conditions by chance to reduce participant bias.

Term
Famous Lab Experiment

Give an example of a famous lab experiment.

Answer
Example

Milgram’s obedience study.

Term
Ethical Concerns in Experiments

What ethical concerns are specific to experiments?

Answer
Ethics

Informed consent, use of deception, avoiding harm, and participant rights.

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🧠 Experiments in Psychology Quiz

1. Which variable is manipulated in an experiment?

The independent variable is the one the researcher changes to observe its effect.

2. What is a major advantage of laboratory experiments?

Laboratory conditions allow researchers to control variables tightly.

3. Field experiments differ from laboratory experiments because:

Field experiments take place in real-world environments, increasing ecological validity.

4. Why are quasi experiments limited in establishing cause-and-effect?

Without manipulation and random assignment, causal conclusions are weaker.

5. Which famous experiment is an example of a laboratory experiment?

Milgram’s study was conducted under controlled lab conditions manipulating variables.

📊 Results

  • Notes and Quiz
  • Psychology
  • AS Level
  • Research Methods
  • OCR