2.1 Research Methods

Cambridge International AS Level Psychology (9990)

2026 📋 Syllabus Objectives

By the end of this topic, you should be able to:

  • Understand and describe the different research methods used in psychology: experiments (laboratory and field), interviews, psychometric tests, case studies, observations, and correlations
  • Understand experimental designs: independent measures and repeated measures
  • Explain key concepts such as independent variable (IV), dependent variable (DV), control, standardisation, and random allocation
  • Understand the different types of observation (overt/covert, participant/non-participant, structured/unstructured, naturalistic/controlled)
  • Understand what correlations are, how to interpret them, and their limitations
  • Understand longitudinal studies and evaluate their advantages and disadvantages

📖 Main Content

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1. Experiments

What is an experiment?

An experiment is a research method used to find out whether one thing causes another. It is the only research method that can show a cause-and-effect relationship — meaning it can tell us whether one variable directly causes a change in another.

In an experiment, the researcher:

  • Changes one variable on purpose
  • Measures how that change affects another variable
  • Keeps everything else the same so that nothing else can explain the result

The Key Variables

  • Independent Variable (IV): This is the variable that the researcher deliberately changes or manipulates. Think of it as the "cause." For example, whether a participant drinks coffee or water.

  • Dependent Variable (DV): This is the variable that the researcher measures. It is what you expect to change as a result of the IV. Think of it as the "effect." For example, how quickly a participant presses a button.

  • Controlled variables: Everything else that could affect the DV must be kept the same across all conditions. This ensures the experiment is a fair test. For example, keeping the room temperature and noise level the same for all participants.

Example: Dr Rox wanted to see whether caffeine affects reaction time.

  • IV: The drink given (300ml of coffee with 100mg caffeine vs. 300ml of plain water)
  • DV: Reaction time, measured in milliseconds on a button-press task
  • Controlled variables: Temperature, lighting, and noise levels in the lab

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