A variable is something you’re trying to measure. It can be practically anything, such as objects, amounts of time, feelings, events, or ideas. If you’re studying how people feel about different television shows, the variables in that experiment are television shows and feelings. If you’re studying how different types of fertilizer affect how tall plants grow, the variables are type of fertilizer and plant height.
There are two key variables in every experiment
The independent variable and the dependent variable. The independent variable is the variable whose change isn’t affected by any other variable in the experiment. Either the scientist has to change the independent variable herself or it changes on its own; nothing else in the experiment affects or changes it. Two examples of common independent variables are age and time. There’s nothing you or anything else can do to speed up or slow down time or increase or decrease age. They’re independent of everything else.
The dependent variable is what is being studied and measured in the experiment. It’s what changes as a result of the changes to the independent variable. An example of a dependent variable is how tall you are at different ages. The dependent variable (height) depends on the independent variable (age).
An easy way to think of independent and dependent variables is, when you’re conducting an experiment, the independent variable is what you change, and the dependent variable is what changes because of that. You can also think of the independent variable as the cause and the dependent variable as the effect.
It can be a lot easier to understand the differences between these two variables with examples, so let’s look at some sample experiments below.
Examples of Independent and Dependent Variables in Experiments
Below are overviews of three experiments, each with their independent and dependent variables identified.
Experiment 1: You want to figure out which brand of microwave popcorn pops the most kernels so you can get the most value for your money. You test different brands of popcorn to see which bag pops the most popcorn kernels.
- Independent Variable: Brand of popcorn bag (It’s the independent variable because you are actually deciding the popcorn bag brands)
- Dependent Variable: Number of kernels popped (This is the dependent variable because it’s what you measure for each popcorn brand)
Experiment 2: You want to see which type of fertilizer helps plants grow fastest, so you add a different brand of fertilizer to each plant and see how tall they grow.
- Independent Variable: Type of fertilizer given to the plant
- Dependent Variable: Plant height
Experiment 3: You’re interested in how rising sea temperatures impact algae life, so you design an experiment that measures the number of algae in a sample of water taken from a specific ocean site under varying temperatures.
- Independent Variable: Ocean temperature
- Dependent Variable: The number of algae in the sample
For each of the independent variables above, it’s clear that they can’t be changed by other variables in the experiment. You have to be the one to change the popcorn and fertilizer brands in Experiments 1 and 2, and the ocean temperature in Experiment 3 cannot be significantly changed by other factors. Changes to each of these independent variables cause the dependent variables to change in the experiments.