Investigation planning

How to Write a Scientific Question

Turn a general observation into a focused, measurable, and testable question that can guide a scientific investigation.

Definition

What is a scientific question?

A scientific question asks about a measurable, observable, or testable relationship. It provides direction for the hypothesis, experimental design, data collection, and conclusion.

A useful question is specific enough to investigate under controlled conditions but broad enough to produce meaningful evidence.

Question structure

A practical scientific-question formula

Question structureHow does [independent variable] affect [dependent variable] under [defined conditions]?

This structure is useful because it identifies what will be changed and what will be measured.

Planning process

Six steps for writing a testable question

01

Choose a focused topic

Begin with a specific scientific phenomenon, material, organism, process, or measurable relationship.

02

Identify the independent variable

Decide what factor will be deliberately changed, selected, or compared.

03

Identify the dependent variable

Decide what response, result, or measurement will be recorded.

04

Define the investigation conditions

Specify the system, material, organism, duration, range, or environment when this improves precision.

05

Check that the question is measurable

Confirm that the result can be observed or measured using available tools, units, and procedures.

06

Check that the question is practical

Ensure the investigation can be completed safely, ethically, and within the available time and resources.

Variables

Identify what changes and what is measured

Independent variable

The factor changed

This is the condition, treatment, amount, or category deliberately changed or compared.

Dependent variable

The response measured

This is the result or outcome recorded to determine the effect of the independent variable.

Worked example

Turn a topic into a scientific question

General topic

Plant growth

This identifies a subject but does not define a testable relationship.

Testable question

How does light duration affect plant height?

The light duration can be changed and plant height can be measured.

  • Independent variable: daily light duration
  • Dependent variable: plant height
  • Possible controlled variables: plant species, soil, water, pot size, and temperature

Question examples

Examples of testable scientific questions

  • How does water temperature affect the time required for sugar to dissolve?
  • How does ramp height affect the distance traveled by a model car?
  • How does salt concentration affect the boiling point of water?
  • How does exercise duration affect heart rate?
  • How does surface area affect the rate of a chemical reaction?

Question quality

Weak questions and improved versions

A

Too broad

Weak: What affects plant growth?

Improved: How does fertilizer concentration affect the weekly height increase of bean plants?

B

Subjective

Weak: Which liquid is best for plants?

Improved: How does irrigation liquid affect the number of leaves produced by bean plants over three weeks?

C

Not measurable

Weak: Do plants like music?

Improved: How does daily music exposure affect the average height of bean plants?

Quality checklist

Check the question before experimenting

  • Is the question focused on one main relationship?
  • Can the independent variable be changed or compared?
  • Can the dependent variable be measured or observed?
  • Can important controlled variables be kept constant?
  • Can the investigation be repeated?
  • Can it be completed safely and ethically?
  • Is the wording clear and free from subjective terms?

Next steps

Review the complete process in Steps of the Scientific Method, then organize the investigation using the Lab Report Template.

Questions and answers

Scientific question FAQ

What makes a scientific question testable?

A scientific question is testable when its variables can be changed, measured, observed, or compared using a practical investigation.

Should a scientific question include variables?

A strong experimental question normally identifies the independent variable and the dependent variable, either directly or through clear wording.

Can a scientific question begin with why?

It can, but why questions are often too broad for a single experiment. Questions beginning with how does or what is the effect of are usually easier to test.

What is the difference between a topic and a scientific question?

A topic identifies a general subject, while a scientific question defines a specific relationship or effect that can be investigated.