Determining Variables and Constants Designing a Controlled Experiment

Variables • Variable: any factor that can change in a controlled experiment • Independent or manipulated variable: the factor that you are testing • The independent variable is expressed in your hypothesis after the word if

Variables con’t • Dependent or responding variable: the factor that you measure to gather results. • It is expressed in your hypotheses after the word then.

Hypothesis • If the amount of fertilizer in lake water is increased, then the amount of algae will also increase, because fertilizers provide nutrients that algae need to grow • What is the independent and dependent variable in this hypothesis?

Controlled Experiment • An experiment in which all factors except one are kept constant • Constants: are all of the factors that are the same in both the experimental group and the control group

Experimental Group and Control Group Experimental Group This is the group where the variable is being tested. Be sure to perform several trials in order to obtain reliable results.

Experimental Group • Example: • Two containers of lake water with one drop of fertilizer solution added to each

Control Group • This group is the same as the experimental group in every way possible, except for the factor being tested is not present here. • Example: • Two containers of lake water with no fertilizer solution added

Variables and Constants in Algae Experiment • Constants • Independent Variable • Amount of fertilizer in • Where the lake water • Dependent Variable • Amount of algae that grow • is obtained • Type of container used Light and temperature conditions where water will be stored

Measuring the Dependent Variable • Operational definition is a description of the one particular way in which you will measure the dependent variable • Operational definition is important for several reasons

Operational Definition • First: in any experiment there are several ways • • in which a dependent variable can be measured Second: the procedure of the experiment depends on how you decide to measure the dependent variable. Third: your operational definition makes it possible for other people to evaluate and build on your experiment

Qualitative Operational Definition • Your measurement of the dependent variable can simply be an observation of whether a change occurs as a result of the independent variable • This type of operational definition can be thought of as a “yes or no” measurement • Easy to do, but does not provide much detail in your experimental results

Quantitative Operational Definition • Measurement of the dependent variable can be a number that shows how much change occurs as a result of the independent variable • This can be more difficult to make and analyze • Provides much more information about your experiment and is often useful