Aim & Hypothesis
Aim & Hypothesis
Navigate the knowledge tree: 🌿 Skills ➡ Designing an Investigation
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Learning Intentions
By the end of this topic, you should be able to:Learning Intentions
Explain the difference between an Aim and a Hypothesis in a scientific investigation.
Write clear, specific, and testable Aims and Hypotheses for different types of investigations.
Use observations and inferences to develop logical hypotheses that can be supported or rejected by evidence.
Glossary
Key terms and definitions.Glossary
aim: A clear statement of what you are trying to investigate or find out during a scientific investigation. It does not predict the result.
hypothesis: An educated guess that explains what you think will happen, based on evidence or prior knowledge. It must be testable.
inference: A scientific explanation or conclusion based on observations and prior knowledge. It can be used to help create a hypothesis.
variable: Any factor in an investigation that can change or be changed.
What is the purpose of an investigation?
What is the purpose of an investigation?
There are many different types of investigations. For example, investigations can be:
Fair testing, where one variable is changed (the independent variable) and another variable is measured as a result of this change (the dependent variable).
Pattern seeking, where an interaction or relationship 'in the field' is investigated under natural conditions (no manipulation takes place, unlike fair testing).
Scientific modelling, where models are used to predict or explain a biological phenomenon.
🌿Go to related content: Types of Investigations
Regardless of the type of investigation chosen, every scientific investigation must have a clear purpose — a clear reason for doing the investigation. This purpose helps keep the investigation focused and makes it easier for others to understand what is being tested.
The purpose is usually expressed in two parts:
Aim → What you are investigating or trying to find out
Hypothesis → What you think will happen, based on evidence or prior knowledge.
The purpose of a scientific investigation must be specific and focused (not too broad), testable (something you can measure or observe), and be based on scientific thinking (not just a guess). Scientists collect data to support or reject their hypothesis — not to “prove” it true. Science remains open to change when new evidence appears.
How to write an aim
How to write an aim
The aim is a short, clear statement that describes the purpose or objective of an investigation. It clearly states what you are trying to find out or achieve through the investigation. It does NOT suggest what the result will be.
The good aim must:
Be written clearly and avoid unnecessary words so it is easy to understand.
Be specific and focuses on one question.
Not make a prediction about the outcome (because that's a hypothesis!)
Includes the independent variable (what you will change) and dependent variable (what you will measure) in fair tests.
🌿Go to related content: Variables
For example:
Instead of: "To find out if plants grow taller in sunlight." (This is a hypothesis)
A better aim would be: "To investigate the effect of sunlight on plant growth."
How to write a hypothesis
How to write a hypothesis
A hypothesis is an educated guess — a possible explanation for what you have observed or what you think will happen. It is based on scientific reasoning, prior knowledge, or research. A good hypothesis must:
Be testable (you can collect measurable or observable data).
Be written before the investigation begins.
Clearly show the expected effect of changing one variable on another.
In all types of investigations, the hypothesis is always written after the aim (purpose) and before the method (procedure). However, the wording of the hypothesis will change depending on the type of investigation.
Observation Investigations
Observation Investigations
In observation investigations (where the goal is to understand things in their natural setting), scientists cannot control the variables. In these cases, a hypothesis is written as:
I think that...
It is still based on evidence and is still testable through further observations.
Hypotheses can be written from inferences
Hypotheses can be written from inferences
Another way to write a hypothesis is to make an inference and then convert that inference to a hypothesis. For example, many parts of New Zealand have a dry season. Grass changes from being green to being brown or yellow. One observation is that the grass does not turn brown as quickly near the edges of a concrete path but remains green for much longer.
We can make an inference, based on our experience and deduced from the facts. An inference is like an educated guess and is a possible answer. A valid inference is one that explains all the observations.
Some inferences that may explain why grass growing near the edge of the concrete path remains green in summer are as follows.
This grass receives the rain runoff from the path when it rains.
The concrete path insulates the grass roots from the heat and cold.
People do not walk on this part of the grass.
The soil under the path remains moist while the soil under the open grass dries out.
More earthworms live under the path than under the open grass.
For Inference 2 above, the hypothesis might be:
If the temperature of the grass roots were measured, then the grass roots under the path would be cooler than the grass roots beside the path.
Fair Test Investigations
Fair Test Investigations
In fair test investigations (where the goal is to determine how changes in one factor affect another), a hypothesis is written after the aim (purpose) and before the method (procedure). The hypothesis must be worded in such a way that it can be tested in an experiment. To write a hypothesis, you will need to identify the dependent and independent variables.
The independent variable is the variable that you, the 'scientist', control or set - what you do.
The dependent variable is the variable that changes depending on what you do. The results of the dependent variable are what you observe or measure.
A good hypothesis should be written in terms of the dependent and independent variables. It should be written like this:
If (I do / change this - independent variable) then (this - dependent variable) will happen.
An example of a hypothesis is:
If I bake potatoes, pumpkin and sweet potatoes at the same temperature, the the pumpkin will cook the fastest.
The 'if' part of the hypothesis is what you believe to be true. The 'then' part is what you will observe if the 'if' part is, indeed true. A correctly written hypothesis will tell you exactly how to conduct the experiment.
A true or valid experiment will test only one hypothesis at a time. If you get this far and realise your question cannot be answered by investigating, you will need to go back and look at whether any part of your question involves something that cannot be measured. If so, rephrase your question so it can be measured.
More on Aim & Hypothesis
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Glossary
Key terms and definitions.Glossary
aim: A clear statement of what you are trying to investigate or find out during a scientific investigation. It does not predict the result.
hypothesis: An educated guess that explains what you think will happen, based on evidence or prior knowledge. It must be testable.
inference: A scientific explanation or conclusion based on observations and prior knowledge. It can be used to help create a hypothesis.
variable: Any factor in an investigation that can change or be changed.
Practice Tasks for Different Thinking Skills
Practice Tasks for Different Thinking Skills
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