What is the primary difference between a Field Experiment and a Natural Experiment?

In a Field Experiment, the researcher actively manipulates the Independent Variable in a natural setting. In a Natural Experiment, the researcher does not manipulate the IV; they observe the effects of an IV that changed due to a naturally occurring event.

How does a Quasi-Experiment differ from a True Experiment regarding participant grouping?

A True Experiment uses random allocation to assign participants to conditions, minimizing bias. A Quasi-Experiment uses pre-existing groups based on inherent traits (like age or occupation), meaning the researcher cannot randomly assign participants.

What is the trade-off between Internal and External Validity in Lab Experiments?

Lab Experiments have high Internal Validity because they control extraneous variables effectively, but they often have low External (Ecological) Validity because the artificial setting may not reflect real-world behavior.

Why is the lack of random allocation a 'Common Error' in interpreting Quasi-Experimental results?

Without random allocation, researchers cannot be certain that the IV caused the change in the DV. The results might instead be caused by 'participant variables'—pre-existing differences between the groups that were not controlled.

What error occurs when a researcher ignores 'Demand Characteristics' in a Lab Experiment?

The researcher may mistakenly attribute behavior changes to the IV, when in reality, participants changed their behavior because they guessed the study's aim and were trying to please or defy the researcher.

Why is it a mistake to assume high Ecological Validity automatically means a study is 'better'?

While high Ecological Validity makes results more generalizable, it often comes at the cost of Internal Validity. If a study is so realistic that it lacks control, the researcher cannot prove that the IV actually caused the effect.

Define 'Independent Variable' (IV) in the context of an experiment.

The Independent Variable is the factor that is manipulated or changed by the researcher (or by nature) to see if it has an effect on another variable. It is the hypothesized 'cause' in the relationship.

What are 'Extraneous Variables'?

Extraneous variables are any variables other than the IV that could potentially affect the DV. If they are not controlled, they can become confounding variables that ruin the validity of the experiment.

Define 'Standardized Procedures'.

Standardized procedures are a set of identical instructions and steps followed for every participant in an experiment. This ensures that all participants have the same experience, reducing the chance of researcher bias or situational variables.

Why are Natural Experiments often considered more ethical than Lab Experiments?

Natural experiments allow researchers to study the effects of potentially harmful or stressful variables (like job loss or trauma) without actually causing them. The researcher simply observes an event that was going to happen anyway.

Types of Experiment | AQA A-Level Psychology

Types of Experiment

Summary

Experimental research is categorized based on the level of environmental control, the method of independent variable manipulation, and the technique used for participant al Understanding these types is essential for evaluating the balance between internal validity (the accuracy of causal conclusions) and external validity (the generalizability of findings to real-world settings).

1. Definition & Core Concepts

The Experimental Method: A research approach where an Independent Variable (IV) is manipulated to observe its effect on a Dependent Variable (DV) while controlling for extraneous variables.
Causality: The primary goal of any experiment is to establish a cause-and-effect relationship, demonstrating that changes in the IV directly result in changes in the DV.
Random Allocation: The process of assigning participants to different experimental conditions by chance, which ensures that participant variables (like intelligence or personality) are distributed evenly across groups.
Standardization: The use of identical procedures and instructions for all participants to ensure that the only difference between groups is the manipulation of the IV.

2. Laboratory Experiments

Controlled Environment: These experiments take place in highly regulated settings where the researcher has maximum control over extraneous variables.
High Internal Validity: Because the researcher can isolate the IV and minimize outside interference, they can be more confident that the IV caused the observed effect.
Low Ecological Validity: The artificial nature of the setting may cause participants to behave differently than they would in real life, making it difficult to generalize results.
Demand Characteristics: Participants in a lab setting are often more likely to guess the aim of the study and alter their behavior to 'help' or 'hinder' the researcher.

A graph showing the inverse relationship between control (Internal Validity) and realism (Ecological Validity) across Lab, Field, and Natural experiments.

3. Field Experiments

Natural Settings: The researcher manipulates the IV in the participants' everyday environment (e.g., a school, workplace, or public street).
Higher Ecological Validity: Because the environment is familiar and natural, the behavior observed is more likely to reflect genuine real-world responses.
Reduced Control: It is much harder to control for extraneous variables (like weather, noise, or interruptions) in a field setting compared to a lab.
Ethical Considerations: Participants are often unaware they are being studied, which raises issues regarding informed consent and the right to withdraw.

4. Natural and Quasi-Experiments

5. Key Distinctions

6. Exam Strategy & Tips