WHAT ARE VARIABLES?
Let us start with a verb: to vary. ‘To vary’ means to alter or change. In a scientific investigation, then, a variable is something that can alter or change. In a scientific investigation, what is most important about any variable is that it is observable and/or measurable. Thus, in science education we sometimes talk about ‘observable’ variables and/or ‘measurable’ variables. Let’s look at a brief example:
The temperature of water in a glass beaker…
Can you imagine observing a change in the temperature of the water inside of a glass beaker? If so, what would it look like? How would you know the temperature is changing by looking at it?
Can you imagine measuring a change in the temperature of the water inside of a glass beaker? What tool (or tools) might help you measure this change?
In the example above, it’s probably best to imagine the temperature of water in a glass beaker as a measurable variable because most of us can imagine using a standard thermometer to measure any change in temperature. It’s harder to imagine the temperature of water in a glass beaker as a observable variable because it’s practically impossible for the human eye to see any visible difference(s) in the appearance water when it’s at, say, 20 degrees C versus 25 degrees C. At best, we might say that the temperature of water in a glass beaker is an observable variable but only because of the help of a measuring device called a thermometer.
Observable/measurable variables sit at the very foundation of all scientific investigations. Typically, you will hear scientists and science teachers talk about no less than three different types of observable/measurable variables:
Which of these variables are present during a scientific investigation depends on the type of scientific investigation in which you are engaged. For example, descriptive investigations make use of an observable/measurable variable that is not considered to be a manipulated, responding or controlling variable. Comparative investigations make use of two observable/measurable variables–manipulated (independent) and responding (dependent) variables. Experimental investigations make use of all three types of observable/measurable variables–manipulated (independent), responding (dependent), and controlling variables.
Last update: March 2016