NSW Science (Years 7 to 10)
Planning and Recording a Valid Investigation: Variables, Tables and Graphs
Many NSW Science students lose easy marks on school assessments not because they lack knowledge, but because they muddle up their variables, draw their table after collecting data, or put the axes of a graph the wrong way around. These are procedural habits, and once you understand the logic behind each step, the marks follow naturally.
What the syllabus asks
The NSW NESA Science 7–10 curriculum asks students to work scientifically across every module, including Observing the Universe. That means planning and conducting valid investigations safely, processing and analysing data, and communicating findings clearly. This concept focuses on the planning and recording side: identifying variables, setting up a results table before you start, and then graphing and interpreting what you find.
The idea, explained
Variables: the heart of a valid investigation
Every investigation involves factors that could change. Science teachers expect you to name three types clearly.
The independent variable is the one factor you deliberately change. You are in control of it. For example, if you are recording how the apparent brightness of a star changes as you move a light source further away, the distance is the independent variable because you are the one moving it.
The dependent variable is what you measure to see the effect of that change. In the same example, the brightness reading is the dependent variable because it depends on what you did with the distance.
Controlled variables are everything else, kept the same throughout. Keeping them constant is what makes the test fair. If you changed two things at once, you could not tell which one caused the result, and the investigation would not be valid. A valid investigation changes only one variable at a time.
Observations over time
Some investigations do not change a physical factor but instead record how something changes over time. In these cases, time is the independent variable. The key rule is to take readings at regular, planned intervals (for example, every minute for ten minutes) rather than whenever it feels convenient. Planning those intervals before you start is part of designing a valid investigation.
Recording results in a table
Draw your table before you collect any data. This is not just good practice; it forces you to think about what you are measuring and in what units before the investigation begins.
The layout follows a simple rule: the independent variable goes in the left column, and the dependent variable goes in the right column. Each column heading must state both the quantity and its unit, written as, for example, Time (min) or Temperature (°C). Record each result immediately and exactly as measured, without rounding or adjusting.
Graphing your results
Once your table is complete, a line graph is the right choice for continuous data (data that can take any value along a scale, such as time or temperature).
The independent variable always goes on the horizontal axis (the x-axis), and the dependent variable always goes on the vertical axis (the y-axis). Both axes need a label that includes the unit. The scale must be even, meaning the gap between numbers is the same all the way along. Plot each point accurately and give the graph a title.
Drawing a conclusion
Look at the shape of the graph and ask: as the independent variable increases, does the dependent variable increase, decrease, or stay roughly the same? Your conclusion must state the relationship you found and answer the original question, using your data as evidence. A conclusion that says "the temperature went down" is weaker than one that says "as time increased, the temperature decreased from 80°C to 22°C over ten minutes, showing that the liquid cooled steadily."
What the exam asks
School assessment questions on this concept typically ask you to:
- Identify the independent variable, dependent variable, or a controlled variable from a described investigation.
- Explain why changing only one variable at a time makes an investigation valid.
- Complete or design a results table with correct headings and units.
- Draw or interpret a line graph, including labelling axes with units and choosing an appropriate scale.
- Write a conclusion that refers to a trend in the data and answers the original question.
Science teachers award marks for precise terminology, so use the words "independent variable", "dependent variable" and "controlled variable" rather than vague phrases like "the thing I changed".
Common mistakes
- Swapping the axes on a graph. The independent variable must be on the x-axis and the dependent variable on the y-axis. Reversing them is one of the most common errors science teachers see.
- Forgetting units in table headings. Writing "Time" instead of "Time (min)" costs marks. The heading must include both the quantity and the unit.
- Drawing the table after collecting data. The table should be set up before the investigation starts. Drawing it afterwards often leads to missing columns or inconsistent headings.
- Naming two independent variables. Saying "I changed the distance and the angle" describes an investigation that is not valid, because you cannot tell which change caused the result. A valid investigation changes only one variable at a time.
- Writing a conclusion without data. A conclusion must refer to actual measurements or trends from the graph, not just restate what you expected to happen.
If you want step-by-step practice with immediate feedback on exactly these skills, Avocado's AI-native tutoring service walks you through each stage in its Planning and Recording a Valid Investigation lessons, tailored to the NSW Science 7–10 curriculum.