Experimental Design in Science Investigations
Students Learning the Process of Designing Science Experiments
Sep 8, 2009
Experimental design focuses on planning an investigation of something that naturally occurs in nature through the deliberate manipulation of a specific variable. This is referred to as the treatment in an experiment. As a treatment is introduced into an investigation, observations and measurements are taken to determine the effect of any change in conditions. This is how scientists conduct experiments – the planned manipulation of a variable to determine how this treatment affects the natural order.
The importance of experimental design on student learning is that they need to learn how to design science experiments to truly understand the ideas and processes of science. Students also develop a better understanding of cause and effect relationships because their planned manipulation of a variable or treatment has caused a change to occur. This change results in ruling out alternative causes, which leads students to drawing conclusions about the consequence of their treatment during examination of experimental findings.
Inquiry Science: A Habit of Mind
Inquiry science is the heart of experimental design. Inquiry teaching and learning involves students in the learning process and is essential to students learning how to design experiments. An advantage of this design process is that students incorporate both basic and integrated science process skills as they conduct an experiment.
The process of inquiry science experiments assists students in constructing a much better understanding of the natural and human-designed worlds. Inquiry is not so much seeking the right answer, because often there is none or more than one, as it is developing the habits of mind that seek appropriate resolutions to questions and issues.
Science Experiments: The Experimental Design Process
As students learn to develop their own experimental design they must be able to answer the most important question of all regarding the design process. What question will this science experiment answer? This includes identifying questions that the design will not answer.
Experimental Question – students must learn to not ask questions that result in a simple answer, such as yes or no. Experimental design questions must be open ended. For example:
What is the impact of acid rain on the growth rate of dandelions during spring?
Variables – once students have identified the question an experiment will answer, the next step in the design process is to identify variables. These include:
- Independent Variable – is what is manipulated or the treatment in an experiment.
- Dependent Variable – is what is observed from the effects of the treatment in an experiment.
- Controlled Variables – are factors that remain constant throughout an experiment. One example is setting up a duplicate experiment which does not receive the treatment.
- Extraneous Variables – influence the relationship between the independent and dependent variables of an experiment, which the student has no control over. These are variables that influence the outcome of an experiment and are undesirable because they add error to an experiment.
A student directly manipulates stress levels in human subjects and measures how those stress levels change heart rate. The independent variable would be the stress and the dependent variable would be the heart rate. Controlled variables include time of day, temperature, location, males or females only, weight of subjects, type of stress tests, and no food intake for 2 hours. Extraneous variables include type of food eaten by subjects, how much sleep the subjects had the previous night, and normal heart rate of subjects.
Hypothesis – the next step in the design process is developing a hypothesis to determine if the experimental design is testable; i.e., are the independent and dependent variables measurable. An example hypothesis is:
If a water solution with the same pH level of acid rain is given to dandelions, then the dandelions will grow less.
Students measure the amount of chemicals added to water to create the normal acid rain pH level for their area, along with the amount of water given to the dandelions. They are also able to measure the amount of growth for the dandelion receiving the acid rain treatment, as compared to a control dandelion not receiving the acid rain treatment.
Final Steps – the next steps in the experimental design process focus on determining how the data will be collected, procedural steps for conducting the experiment, and identifying factors that determine if the hypothesis was supported or not supported by experimental findings.
Making Connections by Designing Science Experiments
Experimental design focuses on investigating something a student wants to determine if a treatment will have an impact on, such as designing a new green product for reducing global warming. The key to determining if a student has developed a deeper understanding of the processes of science experiments is when the student is able to redesign the experiment for additional treatment testing. The student is now on the way to mastery of the science problem solving.
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