WACE Psychology — Science inquiry
Experimental Design — Flashcards & Quiz
Experimental design is part of the Science inquiry strand of the WACE Psychology ATAR Year 12 syllabus, taught across Unit 3 and Unit 4. You need to identify the independent, dependent, controlled, extraneous and confounding variables; write directional and non-directional hypotheses; describe an experiment with control and experimental groups; explain random allocation and techniques that reduce extraneous variables (placebos, single-blind and double-blind procedures, standardisation); and evaluate research using internal and external validity.
Key Points
- Independent variable (IV): what the researcher manipulates. Dependent variable (DV): what is measured to see the effect of the IV.
- Control variables are held constant. Extraneous variables (participant, environment, researcher) could affect the DV; a confounding variable has actually affected it, so the result cannot be linked to the IV.
- An experimental design compares an experimental group, which receives the IV, with a control group, which does not.
- Random sampling decides who is in the sample; random allocation decides which group each participant goes into.
- Placebo effect, experimenter effect and demand characteristics are reduced with placebos, single-blind and double-blind procedures, and standardised procedures and instructions.
- Internal validity: did the study measure what it claimed, free of confounds? External validity: do the results generalise to other people and settings?
Common Mistakes to Avoid
- Confusing the IV (cause) with the DV (effect).
- Calling every extraneous variable a confounding variable — it is only confounding if it has systematically affected the DV.
- Using "random sampling" (how participants are chosen) interchangeably with "random allocation" (how they are assigned to groups).
- Mixing up single-blind (participants unaware of their group) and double-blind (participants and the researcher unaware).
- Confusing validity (measuring what it claims) with reliability (consistent results, such as test-retest or inter-rater).
Exam Strategy
The Year 12 ATAR examination samples both the Psychological knowledge and understanding strand and the Science inquiry strand from Units 3 and 4, and science inquiry questions are often set around a described study. Method: (1) state the aim, IV and DV precisely (operationalised), (2) write a hypothesis that names both variables, (3) identify an extraneous variable and say how it could become confounding, (4) name a control that minimises it, and (5) evaluate internal and external validity and suggest an improvement.
Sample Flashcards
Q1: Define the independent variable and the dependent variable, with an example.
The independent variable (IV) is the factor the researcher deliberately manipulates to test its effect. The dependent variable (DV) is the factor measured to see whether it changes because of the IV. In a study of whether sleep loss affects memory, the IV is the amount of sleep (4 hours or 8 hours) and the DV is the number of words correctly recalled.
Q2: Distinguish extraneous variables from confounding variables.
An extraneous variable is any variable other than the IV that could affect the DV, such as participant variables (age, ability), environmental variables (noise, time of day) or researcher variables (tone of voice). A confounding variable is one that has actually affected the DV systematically, differing between groups, so the researcher cannot tell whether the IV or the confound caused the result.
Q3: What is the difference between random sampling and random allocation?
Random sampling is a way of selecting participants from the population so that every member has an equal chance of being chosen, which helps the sample represent the population. Random allocation happens after selection: each participant has an equal chance of being placed in the experimental or control group, which spreads participant variables evenly across groups and reduces confounding.
Q4: How do single-blind and double-blind procedures reduce bias?
In a single-blind procedure participants do not know whether they are in the experimental or control group, reducing demand characteristics and the placebo effect. In a double-blind procedure neither the participants nor the researcher collecting data knows, which also removes the experimenter effect, where the researcher's expectations unintentionally influence participants' responses or how results are recorded.
Q5: What is the role of a control group and a placebo in an experiment?
The control group does not receive the IV, providing a baseline to compare with the experimental group. Any difference in the DV can then be linked to the IV. A placebo is a fake treatment, such as a sugar pill, given to the control group so that both groups have the same expectations, which separates the real effect of the IV from the placebo effect.
Revision Tip
Research methods terms reward instant recall — drill IV, DV, extraneous, confounding, random allocation and the blind procedures with a Revizi deck.
Related Concepts
Last updated: 9 October 2026 · 6 sample flashcards