Planning research: aims and hypotheses (directional and non-directional, the null hypothesis), experimental methods (laboratory, field and natural experiments), and experimental designs (independent measures, repeated measures and matched pairs).

What this dot point is asking

OCR wants you to explain how psychologists plan research: writing aims and hypotheses (directional, non-directional and the null hypothesis), choosing an experimental method (laboratory, field or natural), and choosing an experimental design (independent measures, repeated measures or matched pairs).

Aims and hypotheses

There are three types of hypothesis you must know:

• Directional (one-tailed) hypothesis: predicts the direction of the difference or relationship. Example: "participants who sleep more will recall more words than those who sleep less." Used when previous research suggests a likely direction.
• Non-directional (two-tailed) hypothesis: predicts that there will be a difference or relationship but not which way. Example: "there will be a difference in the number of words recalled by those who sleep more and those who sleep less." Used when there is no clear prior direction.
• Null hypothesis: predicts there will be no difference or relationship (any result is due to chance). Example: "there will be no difference in words recalled." Researchers test whether they can reject the null hypothesis.

Experimental methods

An experiment manipulates an independent variable (IV) to see its effect on a dependent variable (DV). There are three types:

• Laboratory experiment: conducted in a controlled setting. Strength: high control of variables, so cause and effect can be established, and it is easy to replicate. Weakness: artificial, so it may have low ecological validity and trigger demand characteristics.
• Field experiment: conducted in a real-world setting (like Bickman). Strength: higher ecological validity (real behaviour). Weakness: less control of extraneous variables and harder to replicate.
• Natural experiment: the IV varies naturally and is not manipulated by the researcher (for example, comparing people before and after a real event). Strength: allows study of variables that could not be manipulated ethically. Weakness: no control over the IV or who is in each condition.

Experimental designs

The design is how participants are allocated to conditions:

• Independent measures: different participants in each condition. Strength: no order effects (no practice or fatigue from doing both). Weakness: participant variables may differ between groups, and it needs more participants.
• Repeated measures: the same participants do all conditions. Strength: controls participant variables (same people) and needs fewer participants. Weakness: order effects (practice or fatigue), which can be reduced by counterbalancing.
• Matched pairs: different participants who are matched on key variables (such as age or IQ). Strength: reduces participant variables without order effects. Weakness: matching is difficult and time-consuming.

Evaluating planning choices

Good planning matters because it determines whether a study can give a clear, trustworthy answer. The strength of careful hypotheses and controlled experiments is the ability to establish cause and effect and to replicate; the weakness is that the most controlled methods are the least realistic. The design choice always trades off order effects (repeated measures) against participant variables (independent measures), with matched pairs a compromise. The best plan matches the method and design to the aim and is aware of the threats to validity, which connects to sampling and variables and ethics.

Try this

Q1. Write a directional hypothesis for a study on caffeine and reaction time. [2 marks]

• Cue. For example, "participants who drink caffeine will have faster reaction times than those who do not."

Q2. Name the three experimental designs. [3 marks]

• Cue. Independent measures, repeated measures and matched pairs.

Q3. Give one weakness of a repeated measures design. [1 mark]

• Cue. Order effects (practice or fatigue), reduced by counterbalancing.