VARIABLES

Anything in the experiment that could be changed and affect the results of the investigation is a variable. Setups of an experiment should have only one variable that is changed at a time. By having only one variable that is changed, you can be fairly certain that the results of the experiment were caused by that one variable. Three types of variables are explained below:

  • Independent variable (One manipulated - CAUSE) - what the investigator is testing; the ONE thing that is changed or manipulated by the scientist.
  • Dependent variable (One responding - EFFECT) – the response to the independent variable that can be observed (qualitative) and measured (quantitative).
  • Constant variables (many) - variables(rules) that are kept the same or constant throughout the experiment. They could be changed, but the scientist keeps them constant so that they will not interfere with the investigation.
  • Control (one) the “norm”- A part of the experiment that does not have the variable being tested and is used for comparison. (Not all experiments have a control.)

PRACTICE 1- Identifying variables: List three variables that could affect the situation.

What variables can affect the number of fish in a lake?

  • Variable 1:
  • Variable 2:
  • Variable 3:

PRACTICE 2 - Three Types of Variables: For the experiment below, specify the independent, dependent, and constant variables.

Students of different ages were given the same puzzle to assemble. The puzzle assembly time was measured.

  • Independent variable (manipulated): ______
  • Dependent variable (responding): ______
  • Constant variables: ______

______

OPERATIONAL DEFINITION

One of the important decisions a scientist must make is to determine how measurement of the variable will be made. The method used to measure the dependent variable is called an operational definition. Once a scientist has decided on a method, that method must be reported to other scientists, so they can test the investigation results. Any scientist can read an operational definition and easily understand or perform the same measurement.

SF Variables – Operational Definition - Hypothesis

PRACTICE 3 - Think of possible operational definitions for the following problems.

A student wants to test the effect of “Don’t Litter” posters on the trash problem at his school. The variable “trash problem” is what the student needs to measure.

A student wants to find out if study affects science grades. The variable “study” and “science grade” must be defined with operational definitions.

  • Study:
  • Science Grade:
  • Study:
  • Science Grade:

PRACTICE 4 -The following investigation contains operational definitions for a variable. Identify the variables and the operational definitions for the variable.

A study was done to determine the effect of distance running on breathing rate. Students ran different distances and the rate of breathing was measured. One group ran ¼ km, a second group ran ½ km, and a third group ran 1 km. Immediately after running, breathing rate was checked by counting the number of breaths taken in one minute.

  • Independent variable (manipulated): ______
  • Dependent variable (responding): ______
  • Constant variables: ______

______

  • Operational Definition: ______

______

______

SF Variables – Operational Definition - Hypothesis

Science Fair Rubric Checklist – Variables/Operational Definition(s)

Expectations- Variables/Operational Definition(s) / Points
  • Typed/ Font 12/Times New Roman/Double-Spaced
  • Heading (5 lines) – Left of page
  • Title “Science Fair Variables/Operational Definition”
  • Three or less spelling/grammatical errors
  • No contractions; no personal pronouns
  • Independent, dependent, constant variables labeled using colons and semi-colons
  • Example
  • Independent: _____
  • Dependent: _____
  • Constant: _____; _____; _____
  • Control variable identified if applicable following above format
  • Independent and dependent variables identified correctly
  • All constant variables listed and correct
  • Operational definition(s) clearly defined and includes unit of measurement
  • Rubric stapled on front (left corner)
  • Parent signature on typed FINAL assignment [Rough(s) draft stapled to back]
/ 15
SCORE

HYPOTHESIS (Prediction)

A hypothesis is a special kind of prediction that forecasts how one variable will affect a second variable. These variables are the independent variable and the dependent variable. Hypotheses express a logical explanation based on observations, background information, or other scientific knowledge. Hypotheses can be tested. Investigators find them useful because they specify an exact focus for an experiment. A hypothesis is an educated guess and is a minimum of two sentences.

Do not use the words “I think”. The hypothesis can be written using the “If…then…” format. This format, while not always necessary, is a helpful way to learn to write a hypothesis. Using the words “increase” and “decrease” (if possible) also adds details to the hypothesis and refines the prediction. Remember to be as specific as possible when describing the changes in variables. Include a second sentence using background information to support your hypothesis.

FORMAT:

If the (independent variable)is [increased/decreased/etc.], then the (dependent variable) will[increase/decrease /vary /etc.]. Based on research…. or Research indicates….

  • Example:
  • Question: Does the temperature of the sea water affect the amount of salt dissolved?
  • Hypothesis: If the temperature of sea water increases, then the amount of salt that will dissolve in that water increases. Based on research, temperature affects the speed at which substances will dissolve.

Water temperature (independent) and amount of dissolved salt (dependent) are the variables used in this hypothesis. The investigator is predicting that warmer water will have more dissolved salt than colder water. An investigator can design an experiment that manipulates the temperature of several samples of water from the same source. Dissolved salt levels can then be measured in each sample.

PRACTICE 5: Identify the variables in the research question, and then write a hypothesis using the “If…, then…” format.

Research Question: To what extent does the depth of LakeMonroe affect water temperature?

  • Independent variable (manipulated): ______
  • Dependent variable (responding): ______
  • Hypothesis: ______

______

Science Fair Rubric Checklist – Hypothesis

Expectations-Hypothesis / Points
  • Typed/ Font 12/Times New Roman/Double-Spaced
  • Heading (5 lines) – Left of page
  • Title “Science Fair Hypothesis”
  • Two or less spelling/grammatical errors
  • Two to threedeclarative sentences
  • No contractions; no personal pronouns
  • Independent and dependent variables clearly reflected in the hypothesis
  • “If – then-” format evident
  • 2nd/3rd sentences: Hypothesis supported by research; detailed explanation of the evidence used to form hypothesis
  • Rubric stapled on front (left corner)
  • Parent signature on typed FINAL assignment [Rough(s) draft stapled to back]
/ 10
SCORE

SF Variables – Operational Definition - Hypothesis