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The Research Process » Planning an Experiment

What you'll learn this session

Study time: 30 minutes

Cambridge spec: 7.8.2

How to plan an experiment from a scenario in an extended response question
How to work out which parts are given and which you must plan
Two worked plans with mark-scheme-style points
A planning checklist you can use in the exam

Over the last few lessons you have learned the parts of an experiment and the steps of the research process. Now you put them together. In Paper 1 Section D, an extended response question of 4 to 6 marks asks you to plan an experiment. Some parts of the plan are given in the scenario, and you plan the rest.

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What the question looks like

The question gives a short scenario and tells you what is already decided. It might give the aim and the independent variable, or the design. You then write a plan for everything else. An extended response is marked on how well your plan is developed, so it needs several linked points, not a list of single words.

Learn this

Do not repeat what the question already gives you. Plan the parts that are missing, and make each part clear enough that another researcher could carry out your study.

The planning checklist

Use this checklist to work out what to write. Each item uses an idea from an earlier lesson, so there is nothing new to learn here. See Operationalising Variables, Experimental Design and Repeated Measures, Independent Measures and Random Allocation and Extraneous Variables and Controls for the details.

🔧 Variables

Say how the independent variable changes, and how the dependent variable is measured. Both are operationalised, for example a score out of 10.

👥 Design

Repeated measures or independent measures. Give a reason, and say how you use counterbalancing or random allocation.

🎓 Sample

Who the participants are, how many, and the sampling technique used to choose them.

📝 Materials

What you need, such as the word list, a timer or a score sheet.

🔒 Controls

Name what you keep the same, such as the time allowed or the room, and say why it matters.

📋 Procedure

Step by step in order, with standardised instructions. Say what is said to participants before and after.

✅ Ethics

Consent, the right to withdraw, confidentiality and a debrief. Match them to the scenario.

📈 Analysis

How the data will be used, such as finding the mean for each condition and comparing them.

You do not need every item in every answer. Look at the marks. A 4-mark question needs about four well-developed points, and a 6-mark question needs more depth and a wider range.

Worked plan 1: doodling and recall

Question

A researcher wants to test whether doodling while listening to a list of names helps students remember them. The researcher has decided on an independent measures design. Plan the experiment. [6 marks]

First, spot what is given: the aim and the design. Now plan the rest.

Mark-scheme-style points

Variables: students in one group doodle while they listen, and students in the other group just listen. The DV is the number of names recalled out of 15.
Sample: 30 students from one school, chosen by an opportunity sample, for example the first 30 students who walk into the school hall for a rehearsal.
Random allocation: each student is given a number and a random number list decides the group, so 15 students go in each group and the groups are similar.
Materials: the same recording of 15 names, paper and pens, and a recall sheet.
Controls: the same recording, the same quiet room and one minute to write the names down for everyone.
Procedure and ethics: students sign a consent form and are told they can stop at any time. The same spoken instructions are read to both groups. Afterwards they are debriefed.
Analysis: work out the mean number of names recalled in each group and compare them.

This is more than enough for 6 marks. Notice that each point says what is done and gives a reason or a detail. For example, random allocation makes the groups similar.

Worked plan 2: a rhyme and a shopping list

Question

A researcher wants to find out if learning a short rhyme helps teenagers remember a shopping list. One group learns the list with a rhyme. The other group learns the list without a rhyme. The researcher is using an independent measures design with 20 students. Plan how the researcher should carry out the experiment. [4 marks]

Here more is given: the IV, the design and the sample size. Do not repeat these. Plan the missing parts.

Mark-scheme-style points

Operationalise the DV: count how many of 12 items each student writes down correctly after 2 minutes of learning (1).
Use random allocation, so that chance decides the group and there are about 10 students in each group (1).
Control the situation: the same list, the same learning time and the same room for both groups (1).
Use standardised instructions, the same for both groups (1). Any one of consent, the right to withdraw or a debrief earns an ethics mark (1).

The sample size is given, so no sample point is needed. Five points are on offer here, and any four gain the marks. Describing how the means would be compared could also earn credit for analysis.

Common mistakes

Repeating what the scenario already gave you. Plan what is missing.
Writing a list of single words, such as "controls, ethics, sample". Say what you would actually do.
Saying "measure memory" without a score. Operationalise it, for example words recalled out of 15.
Forgetting the scenario. Use its details, such as the people and the task, in your plan.
Writing too little for a 6-mark question. Add depth with a reason for each choice.

Exam-style question

A researcher wants to test whether a short walk outside helps teenagers spell more words correctly in a test. Each teenager will do a spelling test after a walk and a different spelling test after sitting indoors. The researcher has chosen a repeated measures design. Plan the experiment. [6 marks]

Model answer

Any six from:

The DV is the number of words spelt correctly out of 20 (1).
Use two different spelling lists of equal difficulty, so the second attempt is not easier from practice (1).
Counterbalance the order, so half do the walk condition first and half do the sitting condition first (1).
Take a volunteer sample, for example 20 students who put their names forward after a class announcement (1).
Control the room, the time allowed and the instructions so they are the same for every condition (1).
Obtain consent, say they can stop at any time and debrief them afterwards (1).
Work out the mean number of words spelt correctly for each condition and compare them (1).

Exam tip

Check the marks, tick off what the scenario has already given, then plan the rest in order: measure, groups, sample, controls, procedure, ethics, analysis.

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