Understanding variables and fair testing is essential for AQA GCSE Food Preparation and Nutrition students completing NEA Task 1. A food investigation should test a clear question by changing one factor, measuring the result and keeping other important conditions the same. This allows you to make a justified conclusion rather than simply describing what happened. In this guide, you will learn how to identify the independent, dependent and control variables, plan a fair test, improve reliability and explain your findings using suitable food examples.
What is a variable?
A variable is a factor that can change in an investigation. For example, when investigating how the amount of fat affects the texture of pastry, the amount of fat is a variable. A strong investigation identifies which variable will be changed, which result will be measured and which conditions must stay the same.
In AQA NEA Task 1, your investigation should explore a relationship between variables linked to the preparation or cooking of food. The question needs to be focused enough to investigate practically. For example, “How does the type of flour affect the volume of bread?” is more useful than “What affects bread?”
The three main types of variable
| Variable | Meaning | Food investigation example |
|---|---|---|
| Independent variable | The factor you deliberately change. | The type of flour used in bread. |
| Dependent variable | The result you observe or measure. | The volume of the baked bread. |
| Control variables | The important factors you keep the same. | The recipe quantity, mixing time, proving time and baking conditions. |
Independent variable
The independent variable is the one factor you choose to change. You should select sensible values or categories that allow a useful comparison. If you are testing the effect of sugar on the browning of biscuits, you could use different quantities of sugar while keeping the rest of the recipe the same.
Do not change several factors at once. If you change the sugar, flour and baking time together, you will not know which change caused the difference in browning.
Dependent variable
The dependent variable is what changes as a result of the independent variable. It must be measured or observed in a consistent way. Depending on the investigation, you might measure mass, height, volume, spread or cooking time. You might also record sensory qualities such as colour, aroma, texture and taste, using a clearly explained scoring system.
Measurements are usually more useful when they are precise and repeatable. For example, “the biscuit was better” is vague. “The biscuit had a darker golden-brown colour and a crisper texture” gives clearer evidence, especially when supported by a score or measurement.
Control variables
Control variables are the conditions that should remain the same so that the test is fair. These could include ingredient quantities other than the independent variable, the equipment used, portion size, preparation method, mixing time, cooking temperature, cooking time and cooling time.
Not every possible factor needs to be listed. Identify the controls most likely to affect your dependent variable. If you are investigating how proving time affects bread volume, the yeast quantity, flour quantity, dough size and baking conditions should be controlled. Proving time is the independent variable and bread volume is the dependent variable.
What makes a food investigation fair?
A fair test changes one independent variable, measures the dependent variable and controls the other relevant conditions. This makes it more likely that any difference in the result is caused by the factor being investigated.
A fair test also needs a clear method. Record the ingredients, quantities, equipment, process and conditions so that the investigation can be repeated. Use the same method for every sample, changing only the independent variable. Label samples carefully and assess them in a consistent order where possible.
Reliability, validity and accuracy
These terms help you evaluate the quality of your evidence.
- Reliability means how consistent the results are. Repeating each test and looking for a similar pattern can improve reliability.
- Validity means whether the investigation actually tests the question it set out to answer. Changing only the intended independent variable supports validity.
- Accuracy means how close a measurement is to the true value. Suitable equipment and careful measuring can improve accuracy.
Repeating an investigation does not automatically make it reliable. You need to use the same method and record the results clearly. If results are very different, consider possible reasons such as uneven mixing, inconsistent portion sizes or difficulty judging a sensory characteristic.
Worked example: investigating fat in pastry
Question: How does the quantity of fat affect the texture of shortcrust pastry?
- Independent variable: the quantity of fat in each pastry sample.
- Dependent variable: the texture of the baked pastry, recorded using observations and an agreed scoring system.
- Control variables: the type and quantity of flour, liquid quantity, pastry thickness, cutter size, baking conditions, cooling time and assessment method.
A suitable method would prepare samples using the same process, alter only the fat quantity, bake the samples under the same conditions and compare their texture after cooling. The conclusion should answer the investigation question and use the evidence collected. It should not claim that one result is always true if the investigation tested only a small range of quantities.
Common mistakes to avoid
- Changing more than one independent variable.
- Calling the result the control variable. The result is the dependent variable.
- Using a vague dependent variable such as “quality” without explaining how it will be assessed.
- Forgetting that sample size, preparation time or cooling time can affect results.
- Writing a conclusion that repeats the method instead of explaining the pattern in the evidence.
- Making a claim that is broader than the results support.
Exam-ready retrieval checklist
- Can you define independent, dependent and control variables?
- Can you identify all three in a food investigation question?
- Can you explain why only one factor should be changed?
- Can you name relevant controls for a practical food test?
- Can you explain how repeating a test may improve reliability?
- Can you use results to write a justified conclusion?
For the current specification and assessment information, check the official AQA Food Preparation and Nutrition specification. Assessment guidance and food-safety advice can change, so use the relevant current AQA, Food Standards Agency, NHS or GOV.UK information when planning practical work.
Frequently asked questions
Can there be more than one control variable?
Yes. A food investigation normally has several control variables. Keep all relevant conditions the same apart from the independent variable.
What if the result is based on taste or texture?
Explain how you will assess it consistently. Use agreed descriptive criteria or a scoring system, and make sure the people assessing the samples understand the scale.
Why is a clear conclusion important?
It shows what the evidence means in relation to the investigation question. A strong conclusion identifies the pattern, refers to results and avoids claims that the test did not prove.