The Independent Variable (IV)

When you’re learning how to do things at school it’s easy to believe that things have always been like this, people have always done things in this way, but that’s not true: uncountable hours have been spent developing thoughts and ideas that are delivered to students, often in boring or uninspiring ways. 

I’m not saying your teachers are boring and uninspiring, not all of them, but often there’s not enough time to tell students about the history of science, how ideas have evolved over time (often taking the wrong path), and how we ended up basing experiments, lab reports and projects on three confusingly named things called Variables. Let’s look at the first one:

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’. 

This can sometimes be confusing, but with practice, after a while you will be super-fast at deciding what the IV is. For example, if your experiment is about ‘How much goldfish grow with different types of food’, is the INvestigation about goldfish, or food?

You may feel you are investigating fish, so they are the IV, but the IV is the one we change, so the clue is in the word different. If you are changing the type of food in the experiment, this is the one thing you are changing: ‘the type of food’.

You might be investigating 3 types of food (eg fish flakes, fish sticks, lettuce), so some students might get confused and say you are changing more than one thing, but the ‘thing’ is the ‘type of food’ so there is just one! The different types are written in the ‘using’ part of the table:

Writing the variables first in a table is one of those steps students are tempted to miss out because they just want to get the lab reported started, finished, and then they can do something they really enjoy :) But this step actually saves time, especially because if you get the variables confused, your whole lab report will be wrong and you’ll have to start again :( 

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

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

You will notice two things: 

1. You don’t need to write "the independent variable is the 1 thing I change",

2. You don’t need to write anything to do with the units (yet).

People reading your lab report will probably know that the IV is the thing you change, so no need to write it every time, you can include it in your table to help fix it in your mind. The units used to measure out the (in this example) fish food, will be used in the Control Variables section (see below).

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. 

How you change the IV has some important outcomes, which change the way you write  your Results and Conclusion sections. This doesn’t matter if your teacher has already told you how to do the experiment but if you are planning your own experiment you should think about this in advance. If you have been told to investigate the effect of food on fish growth, for example, you could choose ‘type of food’ as we have talked about above, but you could also choose to investigate the amount of food. 

Because you can only change one thing, you would have to choose one type of food to concentrate on, but it means your graph will be different, and your conclusion will be written differently. See our effects of continuous and discontinuous variables on graphs and conclusion page for an in-depth explanation. Briefly, type of fish food will probably have a bar graph, and amount of food will have a line graph; can you see why? 

So, in summary, to make the conclusion section easy (and make your experiment a FAIR TEST) we only change ONE THING, and we call it the IV.

New blog pages that offer unrivalled free-to-use content are being added each week, so make sure you join our mailing list or follow us on social media (facebook and instagram) to keep up-to-date with new developments on the ABEL site.

If you are interested in personalised, individual attention — and you want specialised help related to your work or studies — click here to find your perfect consultant. 

Alternatively, if you have specific questions about the company or you have a specific request, please contact us here, or at: info@abel-consultants.com or on 0034 673395438.