Apply research methods, variables, sampling and ethics to evaluate psychological studies.

What this dot point is asking

Psychology is an empirical science, so it relies on systematic, controlled methods. This dot point is about the toolkit researchers use and how to judge a study's quality.

Research methods

• Experiment: manipulates an independent variable to measure its effect on a dependent variable; the only method that can establish cause and effect. Laboratory experiments have high control; field experiments take place in real settings with more realism but less control.
• Correlational study: measures the relationship between two variables without manipulation. A correlation can be positive, negative or zero, but correlation does not prove causation.
• Observation: watching and recording behaviour, either naturalistic or controlled, overt or covert.
• Case study: an in-depth study of one person or small group (e.g. the amnesiac patient H.M.), rich in detail but hard to generalise.
• Self-report: surveys and interviews gathering people's own accounts, efficient but vulnerable to social desirability bias.

Variables and hypotheses

The independent variable (IV) is manipulated; the dependent variable (DV) is measured. Extraneous variables are unwanted variables that could affect the DV; if they systematically vary with the IV they become confounding variables.

An operational definition states exactly how a variable is measured (e.g. "aggression measured as number of physical contacts in 10 minutes"), making the study replicable.

Experimental design and control

Common designs include independent groups (different participants in each condition), repeated measures (same participants in all conditions), and matched pairs (participants matched on key characteristics). Control techniques include random allocation to conditions, standardised procedures, counterbalancing (to offset order effects in repeated measures), and single- or double-blind procedures.

Sampling

The population is everyone the researcher is interested in; the sample is who actually takes part. Techniques include:

• Random sampling: every member has an equal chance; reduces bias.
• Stratified sampling: the sample reflects subgroups in the population in proportion.
• Systematic sampling: selecting every nth person.
• Convenience (opportunity) sampling: whoever is available; quick but biased.
• Self-selected (volunteer) sampling: people respond to an advert; may attract atypical participants.

A representative sample supports generalisation to the population.

Validity and reliability

Validity is whether the study measures what it claims. Internal validity is whether the IV really caused the change in the DV (threatened by confounds). External validity is whether results generalise to other people (population validity) and settings (ecological validity). Reliability is consistency: would the same procedure produce the same results again? Test-retest and inter-rater reliability are two checks.

Ethics

Australian psychological research follows ethical guidelines (the National Statement and the Australian Psychological Society Code of Ethics). Key principles:

• Informed consent: participants agree knowing the study's nature.
• No undue deception, and debriefing afterward if any deception is used.
• Right to withdraw at any time, including their data.
• Protection from harm (physical and psychological).
• Confidentiality and anonymity of data.

Putting it together

When asked to design a study, state the method, IV, DV, hypothesis, sample and controls, then identify the ethical safeguards. When asked to evaluate a study, work through its validity, reliability, sampling and ethics, giving a balanced judgement rather than a one-sided list.