Writing A Hypothesis

What Is a Real Hypothesis?

A hypothesis is a short statement that proposes a possible explanation to some phenomenon or event

A Hypothesis Must Be….

In order to be considered valid, a hypothesis a) Must Be Testableb) Must Avoid Opinion or Biasc) Is Usually Written As An If…Then…Because

Statement.d) A hypothesis avoids personal

pronouns (I, Me, We, You).e) If… (the independent variable),

then… (the dependent variable)

A Hypothesis is Testable• You will perform a test of how two variables might

be related. • When you are doing a real experiment, you are

testing variables. • Usually, a hypothesis is based on a previous

observation. – Example: You notice that in November many trees

undergo color changes in their leaves and the average daily temperatures are dropping.

– Are these two events connected? – How?

How Is A Hypothesis Written?

Answering the above observation by writing, temperature may cause leaves to change color, does not suggest how you might prove it.

A proper hypothesis is written as an If…then…because statement.

If…Then…Because• If leaf color change is related to temperature ,

then exposing plants to low temperatures will result in changes in leaf color because cooler weather causes a chemical change in the leaf.

Example:If skin cancer is related to ultraviolet light , then

people with a high exposure to UV light will have a higher frequency of skin cancer because UV rays cause radiation that damages a cell’s DNA.

If…Then…BecauseYour hypothesis will use both your independent

and dependent variablesIndependent Variable (manipulated): The

variable controlled by the tester. (IV)

Dependent Variable(responding): The resulting variable from changing the independent variable. (DV)

• In the first example, the independent variable was exposing the leaves to cooler temperatures. The dependent variable is a change in the leaf color.

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Example:A hypothesis is a possible answer to a question.• Question:– What effect does stirring have on solution rate?

• Answer:– If the water is stirred, then the tablet will dissolve

faster because stirring increases solution rate.– IV: Stirring the water faster– DV: The rate the tablet dissolves

Examples• Write a possible hypothesis for the following

questions:

1) Do you think the water quality will be better in some areas of the world or worse?

2) Are the organisms found in the water the same all over the world? Why or why not?

3) What effect does the amount of light have on plant growth?

4) Does the type of metal effect how hot it can become?