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.
If the (independent variable) is [increased/decreased/etc.], then the (dependent variable) will [increase/
decrease /vary /etc.]. Based on research . . . or Research indicates . . .
• 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 Lake Monroe affect water temperature?
• Independent variable (manipulated):
• Dependent variable (responding):
Science Fair Rubric Checklist – Hypothesis
Typed/Font 12/Times New Roman/Double-Spaced
Heading (5 lines) – left of page
o Title “Science Fair Variables/Operational Definition”
Two or less spelling/grammatical errors
Two to three declarative 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 assignment