Define Your Variables

3 - Construct a Hypothesis

A hypothesis is an educated guess about how things work. It is an attempt to answer your question with an explanation that can be tested. A good hypothesis allows you to then make a prediction: "If _____[I do this] _____, then _____[this]_____ will happen.”

Task #3A: Define Your Variables

1. Read What are Variables? to review the types of variables in a scientific experiment.
2. Answer the following questions to check your learning:
   1. Which of the following correctly defines the independent variable, dependent variable, and controlled variable in an experiment?
      Independent variable: the factor that is measured; Dependent variable: the factor that is kept constant; Controlled variable: the factor that is intentionally changed

      Independent variable: the factor that is kept constant; Dependent variable: the factor that is intentionally changed; Controlled variable: the factor that is measured

      Independent variable: the factor that is intentionally changed; Dependent variable: the factor that is measured; Controlled variable: the factors that are kept constant

      Independent variable: the factors that are kept constant; Dependent variable: the factor that is intentionally changed; Controlled variable: the factor that is measured
      Correct! The independent variable is the factor that is intentionally changed, the dependent variable is the factor that is measured, and controlled variables are the factors that are kept constant.
      Nice try! Review the definitions to understand the difference between each type of variable.
   2. Why are controlled variables important in an experiment?
      They help to make the experiment more interesting.

      They ensure that the experiment tests only the independent variable.

      They are the variables that the scientist changes.

      They are not necessary for most experiments.
      Correct! Controlled variables ensure that the experiment tests only the independent variable, allowing for accurate and reliable results.
      Nice try! Review the section on controlled variables to understand their importance.
   3. In the experiment "Does using fertilizer help a plant grow bigger?", what is the independent variable?
      The growth of the plant

      The type of plant

      The amount of water given to the plant

      The amount of fertilizer used
      Correct! The amount of fertilizer used is the independent variable because it is what the scientist changes in the experiment.
      Nice try! Review the example experiments to understand how to identify the independent variable.
   4. In the experiment "When we heat water, does it make it easier for more sugar to dissolve in it?" which of the following is NOT a controlled variable?
      The temperature of the water

      The type of sugar used

      The amount of stirring

      The amount of water
      Correct! The temperature of the water is not a controlled variable because it is what the scientist changes to observe its effect on sugar dissolution.
      Nice try! Review the example experiments to understand the concept of controlled variables and how they differ from the independent variable.
3. Fill out the form below with your project question and variables. You defined these first in Ask a Question, but they may need to be refined or changed based on your background research.
   
   NOTE: If you are using a Science Buddies project, be sure to read the entire project carefully before completing this step.

   • Project Question - If you don’t remember your question, look back at Ask a Question or Background Research. The question should include both the independent and dependent variables.

   • Independent Variable - This is what you change. Remember, most good experiments only change one thing. 

   • Dependent Variable - This is what you measure or observe in your experiment. The dependent variable changes as a result of a change in the independent variable.
   • Controlled Variables - These are the things you need to be sure to keep constant so that you are only testing a single independent variable. Note that this is different from a control group, which is the normal condition against which you compare your experimental results.
   • Remember to document your question and variables in your lab notebook.
   Project Question
   Independent Variable (what you change)
   Dependent Variable (what you measure or observe)
   Controlled Variables (what you keep the same)