To find the dependent variable in an experiment, that's always the data that you collect. And you can remember that because D for data. So what is the data being collected here? This data shows how screen brightness affects a phone's battery life.

You can set your brightness to different amounts from 20 to 100%. Find out how many hours the battery lasts or the battery life. So again, what are we collecting here?

Well, if you set your brightness level to 20%. It looks like this battery is going to last about 16 hours. And that's the data that we collected. How many hours the phone lasts, or the battery life for the device. So this is the data that we're interested in.

And battery life is the dependent variable. Same thing as what we're finding out at the end of the experiment. Now, another way to find it if you're given a graph is you could just redraw these axes

one for the y-axis, one for the x-axis, and then you can turn these into letters. The one that goes up and down, you could turn this into the letter D, and that's always where the dependent variable goes. So, just like we thought, battery life goes up and down.

That's the dependent variable. But the one on the bottom, you could turn this into an I and that's the independent variable. So in this case, screen brightness, that's the thing on the bottom. That's the independent variable. So there we go. There's two ways to find the dependent variable.

Look for the data that you collect, or look for the thing that goes up and down on a graph. But how do you find the independent variable if you're not given a graph? Let's look at an example. Let's look at the word independent. If you're independent, then you have control and you can make changes that you want.

That's exactly what an independent variable is. It's the thing that you change in an experiment. So, let's see what it is for this one. Researchers study how background color affects reading speed. A screen's background color is changed between trials. But there it is.

They tell us the thing being changed is the background color of the screen. So automatically this is the independent variable, the thing that they're changing here. So A, that's the correct option. But, they've given a nice summary. So let's just double check and see what each of these things might be.

The first one, 5 background colors are being used on the screen for reading. Well, they're choosing the background colors. Therefore, that is the independent variable. Okay. Next, the same font and size are used for the text. Now, they're choosing the font and the size. Doesn't that seem like something that they have control over?

Well, the problem is they're the same, so they're not actually changing. Therefore, it can't be an independent variable when things are the same. These ones are called constants. Notice the word variable. it has the word vary in it and that means to change. So it definitely can't be a variable if it's the same of something.

So those are just constants but they're not independent or dependent. They're just a separate thing. Okay. And then lastly, well whatever is being recorded, same thing as the data we collect. So this will be the dependent variable. And here we're collecting data on the time it takes somebody to read a page.

So there we have that one. But again, the only thing that we changed as the experimenter were the background colors. So that's why this one is the independent variable. Okay. This time we're going to look at both independent and dependent variables. Which one is which here? Well, we know we control the independent. We know the dependent is the data we collect.

So let's find both of these here. A study tests how water acidity affects shell strength in clams. Clams are raised in water with different pH levels (acidity), and shell strength is measured. All right. What are they controlling here? It looks to be the pH level or how acidic the water is that the clams are raised in.

So this is the thing that they're controlling. That's the independent variable. Okay. But then the dependent variable, the data they're collecting, same thing as what they're measuring. And in this case, it's the shell strength, how strong the clams' shells are. That's a tongue twister, but we found both of them here. So, let's go ahead and summarize these.

Experimenters changed the pH level and found out whether it affects the shell strength of the clams. So, that was the thing they changed. That's the data that they're interested in. So, both of those are the correct variables here. All righty. And one last one. Once again, we're finding the independent variable. Feel free to pause and try this one on your own. Okay. What are we changing or controlling in this experiment? Let's see.

Scientists tested how fertilizer affects plant growth. Four groups of corn plants were given 4 types of fertilizers. All plants were given the same amount of water and sunlight. After 30 days, the height of each plant was measured. Okay. What are they controlling in this experiment or changing? Well, you know it. It's the type of fertilizer that's being used, because they're choosing which fertilizer to give to which group of corn plants. So, that's the independent variable here – the thing you manipulate.

Now, they're also controlling the amount of water and sunlight they give them. How come these aren't the independent variable? But just like we talked about, it's because those are given in the same amounts each time. They're not actually changing. So, these can't be the independent. They're the constants. And finally, the height of each plant that's being measured. That's the data that's being collected. So, the height of each plant is the dependent variable. But the main thing that we changed that was the type of fertilizer. So B, that's the correct option here.