Class practical: experiment

In one line: Your class runs one small experiment of its own. Paper 2 then asks you about it, so you need its details.

The IB asks every class to run four small studies, called class practicals. One of them is an experiment, usually about learning or memory.

It can be a true experiment or a quasi-experiment. It needs at least 5 people if everyone does both conditions, or 10 if each person does one.

Remember: In the exam you write about your own practical. The two on this page show you how.

Key idea: One of the IB's suggested experiments asks a question every student has: does music help or hurt memory?

The idea comes from the Mozart effect. Later studies found the effect small and hard to repeat, so it is a good question for a class to test.

Sample results: These numbers are sample results to show what a record looks like. In the exam, use your own class's numbers.

How this is asked: Paper 2 Section A asks four questions about one of your practicals. The first two are worth 4 marks each: describe how you used the method, then explain one concept in relation to it.

Exam tip: Every sentence should carry a detail of the practical: a number, a condition or a step.

How this is asked: The last two questions are worth 6 marks each. One compares your method with another method; the other asks you to plan a study with a different method on the same topic.

Exam tip: In a design, every decision gets its reason, in a sentence of its own.

Key idea: Another IB suggestion asks whether one word in a question can change what people remember.

In 1974, Loftus and Palmer showed students films of car crashes. Then they asked how fast the cars were going when they smashed into each other, or hit, collided, bumped or contacted.

Only that verb changed. With "smashed" the average estimate was about 41 miles per hour; with "contacted" it was about 32. The question had changed the memory.

Watch out: this one uses deception: Students were not told that the question wording was the thing being tested.

That is allowed only if it is mild and followed at once by a debrief, which your answer on ethics should say.

Same questions, new practical: The four questions stay the same. What changes is the concept in Question 2 and the method you compare with in Question 3. Here: causality, and a survey.

Exam tip: Say exactly what was changed and what was kept the same. That is what makes a claim about cause.