Investigation Purpose and Variables

Navigate the knowledge tree: 🌿 Biology ➡ NCEA Level 2 Biology ➡ 2.1 Investigation ➡ Lesson 3: Investigation Purpose and Variables

Learning Intentions

By the end of this topic, you should be able to:

Write an aim that clearly describes what my investigation is trying to find out.
Write a hypothesis that makes a testable prediction based on science ideas.
Identify and describe independent, dependent and control variables.
Design a fair test by controlling variables to ensure valid results.

Glossary

Key terms and definitions.

aim: A clear statement that explains what the investigation is trying to find out.

conclusion: A statement that explains what the results show and whether the hypothesis was supported.

control variables: The factors that are kept the same to make sure the test is fair.

dependent variable: The variable that is measured in the investigation.

fair test: An investigation where only one variable is changed and all others are controlled.

hypothesis: A testable prediction that explains what you think will happen and why.

independent variable: The variable that is changed on purpose in an investigation.

reliable results: Results that are consistent and repeatable.

valid results: Results that are accurate and caused by the variable being tested.

variable: Any factor that can change in an investigation.

How to write a clear aim

An aim explains what your investigation is trying to find out. It should be short, clear, and focused on the relationship you are testing.

A good aim:

Starts with “To investigate…”
Names the independent variable (what you change)
Names the dependent variable (what you measure)

How to write a testable hypothesis

A hypothesis is a prediction about what you think will happen in the investigation. It must be:

Based on science ideas (not a guess)
Testable using the method
Linked to your aim

A useful structure is:

If (independent variable changes), then (dependent variable will change), because (give a science reason).

What are the different types of variables

Variables are the parts of the investigation that can change.

Independent variable

The one thing you change on purpose, and usually appears on the x-axis of a graph.

E.g. The sugar concentration of the solution.

Dependent variable

The thing you measure, and usually appears on the y-axis of a graph. It may or may not change because of the independent variable.

E.g. Change in mass of raisins.

Control variables

Things you keep the same to keep the test fair. It prevents other factors from affecting the results.

E.g. Size of raisins, time soaked, temperature.

How to design a fair test

In fair test investigations the goal is to determine what changes in one factor (the independent variable) have on another factor (the dependent variable).

So a fair test means:

Only one variable is changed
All other variables are controlled
Results can be trusted and explained scientifically

If control variables are not managed, results may be unreliable and you won't know what exactly caused any changes seen. As a result, conclusions made about the results may not be valid.

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