5 Manipulated and Responding Variables
“Chirp, chirp, chirp.” It is one of the hottest nights of summer and your bedroom windows are wide open. On most nights, the quiet chirping of crickets gently lulls you to sleep, but not tonight. The noise from the crickets is almost deafening. “Chirp, chirp, chirp, chirp, chirp! ”Why do all the crickets in your neighborhood seem determined to keep you awake tonight? Could the crickets be chirping more because of the heat? How could you find out?
How could you explain your observation of noisy crickets on that summer night? “Perhaps crickets chirp more when the temperature is higher,” you think. In trying to answer the question, you are in fact developing a hypothesis. A hypothesis (plural: hypotheses) is a possible explanation for a set of observations or answer to a scientific question. In this case, your hypothesis would be that cricket chirping increases at higher air temperatures.
It is important to realize that a hypothesis is not a fact. Instead, it is only one possible way to explain a group of observations. In the case of the crickets, perhaps they only sounded louder that night because you had left more windows open than you usually do. Or, maybe there were more crickets around that night.
In science, a hypothesis must be testable. This means that researchers must be able to carry out investigations and gather evidence that will either support or disprove the hypothesis. Many trials will be needed before a hypothesis can be accepted as true.
To test your hypothesis, then, you will need to observe crickets at different air temperatures. All other variables, or factors that can change in an experiment, must be exactly the same (must be exactly the same). Other variables include the kind of crickets, the type of container you test them in, and the type of thermometer. By keeping all of these variables the same, you will know that any difference in cricket chirping must be due to temperature alone.
The one variable that is purposely changed to test a hypothesis is called the manipulated variable (also called the independent variable). In your cricket experiment, the manipulated variable is the air temperature. The factor that may change in response to the manipulated variable is called the responding variable (also called the dependent variable). The responding variable here is the number of cricket chirps.
An experiment in which only one variable is manipulated at a time is called a controlled experiment. Notice that identical containers, thermometers, leaves, and crickets are used in each setup. In one container, the temperature will be maintained at 15°C. In the other two containers, the temperatures will be kept at 20°C and 25°C.
How could you explain your observation of noisy crickets on that summer night? “Perhaps crickets chirp more when the temperature is higher,” you think. In trying to answer the question, you are in fact developing a hypothesis. A hypothesis (plural: hypotheses) is a possible explanation for a set of observations or answer to a scientific question. In this case, your hypothesis would be that cricket chirping increases at higher air temperatures.
It is important to realize that a hypothesis is not a fact. Instead, it is only one possible way to explain a group of observations. In the case of the crickets, perhaps they only sounded louder that night because you had left more windows open than you usually do. Or, maybe there were more crickets around that night.
In science, a hypothesis must be testable. This means that researchers must be able to carry out investigations and gather evidence that will either support or disprove the hypothesis. Many trials will be needed before a hypothesis can be accepted as true.
To test your hypothesis, then, you will need to observe crickets at different air temperatures. All other variables, or factors that can change in an experiment, must be exactly the same (must be exactly the same). Other variables include the kind of crickets, the type of container you test them in, and the type of thermometer. By keeping all of these variables the same, you will know that any difference in cricket chirping must be due to temperature alone.
The one variable that is purposely changed to test a hypothesis is called the manipulated variable (also called the independent variable). In your cricket experiment, the manipulated variable is the air temperature. The factor that may change in response to the manipulated variable is called the responding variable (also called the dependent variable). The responding variable here is the number of cricket chirps.
An experiment in which only one variable is manipulated at a time is called a controlled experiment. Notice that identical containers, thermometers, leaves, and crickets are used in each setup. In one container, the temperature will be maintained at 15°C. In the other two containers, the temperatures will be kept at 20°C and 25°C.
The Importance of Controlling Variables
Suppose you decide to test the crickets at 15°C in the morning and the crickets at 20°C and 25°C in the afternoon. Is this a controlled experiment? The answer is no. Your experiment would have two variables—temperature and time of day. Would increased chirping be due to the temperature difference? Or are crickets more active at certain times of day? There would be no way to know which variable explained your results.
Suppose you decide to test the crickets at 15°C in the morning and the crickets at 20°C and 25°C in the afternoon. Is this a controlled experiment? The answer is no. Your experiment would have two variables—temperature and time of day. Would increased chirping be due to the temperature difference? Or are crickets more active at certain times of day? There would be no way to know which variable explained your results.