Database results:
    examBoard: AQA
    examType: GCSE
    lessonTitle: Laboratory Experiments
Psychology - Cognition and Behaviour - Research Methods - Designing Research - Laboratory Experiments - BrainyLemons
« Back to Menu 🧠 Test Your Knowledge!

Designing Research » Laboratory Experiments

What you'll learn this session

Study time: 30 minutes

  • What laboratory experiments are and how they work
  • The key features of laboratory experiments
  • How to design effective laboratory experiments
  • Strengths and limitations of laboratory experiments
  • Examples of famous laboratory experiments in psychology
  • How to evaluate laboratory experiments

Introduction to Laboratory Experiments

Laboratory experiments are a key research method in psychology. They allow researchers to test cause and effect relationships in a controlled environment. In this session, we'll explore how laboratory experiments are designed, their features and when they should be used.

Key Definitions:

  • Laboratory experiment: A research method conducted in a controlled setting where the researcher manipulates one variable to see its effect on another.
  • Independent variable (IV): The variable that is manipulated by the researcher.
  • Dependent variable (DV): The variable that is measured to see if it changes when the IV is manipulated.
  • Extraneous variables: Any variables other than the IV that might affect the DV.
  • Control variables: Variables that are kept the same for all participants.

🔬 Key Features of Laboratory Experiments

Laboratory experiments have several important features:

  • They take place in controlled environments
  • They involve manipulation of variables
  • They allow for the establishment of cause and effect
  • They can be replicated by other researchers
  • They use standardised procedures

📝 Designing a Laboratory Experiment

When designing a laboratory experiment, you need to:

  • Identify your research question
  • Decide on your IV and DV
  • Control extraneous variables
  • Choose your participants
  • Decide how to allocate participants to conditions
  • Create standardised instructions

Experimental Designs

There are three main types of experimental designs used in laboratory experiments. Each has its own strengths and weaknesses.

👥 Independent Groups

Different participants are used in each condition of the experiment.

Strengths: No order effects, simpler to organise

Weaknesses: Participant variables can affect results

👤 Repeated Measures

The same participants take part in all conditions of the experiment.

Strengths: No participant variables, fewer participants needed

Weaknesses: Order effects can occur (boredom, practice, fatigue)

👫 Matched Pairs

Participants are matched on key characteristics and then split between conditions.

Strengths: Reduces participant variables, no order effects

Weaknesses: Difficult to match participants perfectly, time-consuming

Controlling Variables

A key feature of laboratory experiments is the control of variables. This helps ensure that any changes in the DV are due to the IV and not something else.

Types of Variables to Control

When designing a laboratory experiment, you need to consider and control:

  • Environmental variables: Temperature, lighting, noise, room layout
  • Participant variables: Age, gender, intelligence, personality
  • Experimenter variables: How instructions are given, experimenter bias
  • Procedural variables: Time of day, order of tasks, equipment used

Control is achieved through standardisation (keeping things the same), randomisation (assigning participants randomly) and counterbalancing (changing the order of conditions).

Case Study Focus: Milgram's Obedience Study (1963)

Stanley Milgram conducted a famous laboratory experiment on obedience to authority. Participants were told they were taking part in a study on learning and were instructed to give electric shocks to a "learner" (actually an actor) when they made mistakes. The shocks increased in strength with each mistake.

The IV was the presence of authority figures giving instructions.

The DV was the level of obedience (measured by how far participants went with the shocks).

Milgram controlled variables by:

  • Using a script for all instructions
  • Having the same laboratory setup for all participants
  • Using the same "learner" (actor) throughout
  • Standardising prompts given when participants hesitated

65% of participants continued to the highest level of shock, showing the power of laboratory experiments to reveal surprising human behaviours.

Strengths and Limitations of Laboratory Experiments

👍 Strengths

  • Control: High level of control over variables
  • Cause and effect: Can establish causal relationships
  • Replication: Can be repeated by other researchers
  • Precision: Allows precise measurement of variables
  • Standardisation: Procedures can be standardised

👎 Limitations

  • Artificial: May lack ecological validity
  • Demand characteristics: Participants may guess the aim and change behaviour
  • Experimenter bias: Researcher may unconsciously influence results
  • Ethical issues: May involve deception or cause distress
  • Sample issues: Often use WEIRD samples (Western, Educated, Industrialised, Rich, Democratic)

Improving Laboratory Experiments

There are several ways to improve the validity and reliability of laboratory experiments:

  • Single-blind procedures: Participants don't know which condition they're in
  • Double-blind procedures: Neither participants nor researchers know which condition participants are in
  • Pilot studies: Test the experiment on a small sample first to identify problems
  • Counterbalancing: Change the order of conditions to control for order effects
  • Random allocation: Assign participants to conditions randomly
  • Operationalisation: Clearly define how variables will be measured

Real-World Application: Loftus and Palmer (1974)

Elizabeth Loftus and John Palmer conducted a laboratory experiment on eyewitness testimony. They showed participants videos of car accidents and then asked questions about what they had seen.

The IV was the wording of the question ("How fast were the cars going when they smashed/hit/contacted/bumped/collided into each other?").

The DV was the estimated speed given by participants.

They found that the verb used in the question affected the speed estimate - "smashed" led to higher speed estimates than "contacted".

This study shows how laboratory experiments can have real-world applications, in this case showing how eyewitness testimony can be influenced by the way questions are asked.

Evaluating Laboratory Experiments

When evaluating laboratory experiments, consider:

  • Validity: Does the experiment measure what it claims to measure?
  • Reliability: Would the results be the same if the experiment was repeated?
  • Generalisability: Can the findings be applied to other people or situations?
  • Ethics: Were participants treated ethically? Was informed consent obtained?
  • Practical issues: Was the experiment cost-effective and feasible?

Remember that while laboratory experiments have high internal validity (they're good at establishing cause and effect), they often have lower ecological validity (they may not reflect real-life situations).

Summary

Laboratory experiments are a powerful research method in psychology that allow researchers to establish cause and effect relationships. They involve manipulating an independent variable and measuring the effect on a dependent variable, while controlling other variables. They have strengths (high control, establishing causality) and limitations (artificial settings, ethical issues). Different experimental designs (independent groups, repeated measures, matched pairs) can be used depending on the research question.

When designing and evaluating laboratory experiments, consider issues of validity, reliability, generalisability and ethics. With careful design, laboratory experiments can provide valuable insights into human behaviour and mental processes.

🧠 Test Your Knowledge!
Chat to Psychology tutor