Variables, the foundations that science – and your lab reports – are built on

Let’s be honest, the names of the Variables you have been taught have terrible names that don’t help you understand what they mean. However, once you have spent some time thinking about them, and not just trying to memorise their names, the basis of the scientific method will literally be part of your brain structure (!) and not only will you be able to boss your lab reports, but outside of school and when you’re an adult you’ll be able to acquire new knowledge and skills more easily.

Sounds great, so what do you need to know?

Variables

All experiments are based on how you change one thing, measure a different thing, and make sure nothing else changes. Why?  Because if you change more than one thing, it gets messy. You can’t say what caused any differences you measured (your conclusion) if you change too many things at the start. 

ABEL INSIGHT: Your teachers can tell if you understand an experiment, know how to write a lab report, and see if you started looking for the right Background Information, just from reading how you have written the Variables section.

The best part is, you can use the same structure for the Variables in every lab report, and they can be planned out using a table:

As you will be writing this out for every experiment, you will be able to quickly write IV, DV, and CVs, but what do these abbreviations stand for?

Types of variables

There is an overview of each type of variable on this page, or click on the different names here to go to a page that gives you more detail about each one.

IV = Independent variable: The 1 thing you CHANGE 

DV = Dependent variable: The 1 thing you MEASURE 

CVs = Control Variables: The multiple things you keep the SAME 

We will go through each of the Variables in a moment, but after a few times of writing the table in full, you will be able to draw the quick version (see below), and you will have to spend less time thinking about what each section means. All steps still need to be completed, you just get better and faster at doing each part–with practice!

ABEL INSIGHT: Tables are a great way to quickly write, show, remember, and revise lots of information, but often you will need to be able to write the information in clear sentences. This Variables table is a great one to use for practice.

The Independent Variable (IV)

There is only ever one independent variable - we can write it as IV. You might try to remember it as:

‘The INdependent variable is the one we INvestigate’. 

For example, if your experiment is about ‘How much goldfish grow with different types of food’, is the INvestigation about goldfish, or food?

Remember the IV is the one thing we change, so the clue is in the word different. If you are changing the type of food in the experiment, the IV must be ‘the type of food’, and you might write it in the table like this:

So, how would you write this part of the table out as a sentence? You could write:

The independent variable is the type of fish food, we will use fish flakes, fish sticks, and lettuce.

This example has 3 different types of food, but you may need to change our IV, three, five, or even more times. Remember to use the markscheme or task instructions properly, so you know how many you need to change and you can get the top marks. 

So, remember, to make writing the conclusion section easy (find out why in the detailed Independent Variable page) and make your experiment a fair test we only change ONE THING, and we call it the IV.

The Dependent Variable (DV)

To make it easy to do the experiment, we only normally measure ONE THING the IV affects, or changes. The thing we measure is called the dependent variable, and we can call it the DV.

The Variables table can really help you understand the role of the DV and the equipment you will use to measure it.

So, how would you write this part of the table out as a sentence?

The dependent variable is the length of the fish, measured in cm, using a ruler that has been submerged in the tank. 

If you spot any problems that might make measurements difficult and possibly change the results, write them down and use them in the Evaluation section, or as part of the Control Variables. See the detailed Dependent Variable page for more information.

The Control Variables (CVs)

This is the only row in the Variables Table that is plural, i.e. you need to write down more than one thing. These are things that could change the result of the experiment and make it an unfair test. Small differences can be smoothed out by calculating the average of your DV measurements, but you need to show how you will keep some things the same, to make it a fair test and minimise these differences. 

There will be a minimum of 3 or 5 Control variables (or CVs) depending on what year you are in, so use the markscheme from the beginning of the experiment to make sure you control a sufficient number of variables. 

If you are working with someone else, or other people in the lab are working on the same or similar experiment, with them Brainstorm what things could change the results of the experiment, and write your best ideas into the Variables Table.

So, how would you write this part of the table out as sentences?

Think about it, then see below for the suggested answer!

A good way to write that part of the table is:

The control variables are the species of the fish Fantail), the amount of food (10 g/day), and how far the camera is away from the tank (10 cm). A box will be placed outside the tank, in line with the ruler inside the tank. A line will be drawn on the box 10 cm away from the glass, this will also make sure the photos are taken at the same angle each time.

If you think of another CV when you are planning, doing, or writing about the experiment, put it in the lab report! Just make sure it goes in the right place: if it is before/when you are doing the experiment it’s a CV, if it is after…….. Not a problem! Put it in the Evaluation section.

That was easy - what’s next?!

That’s it, these are your 3 types of variables. Wait, remember we said that the names of the variables are confusing? Well, there is another one that you may be asked to think/write about, which sounds very similar to the CVs: Control Variables.

However, a controlled variable is not a Control Variable (CV).

Confused? Don’t worry, head over to the ABEL Controls in Experiments page to find out more! 

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