The null hypothesis may be the most valuable form of a hypothesis for the scientific method because it is the easiest to test using a statistical analysis. This means you can support your hypothesis with a high level of confidence. Testing the null hypothesis can tell you whether your results are due to the effect of changing the dependent variable or due to chance.

### What Is the Null Hypothesis?

The null hypothesis states there is no relationship between the measured phenomenon (dependent variable) and the independent variable.

You do not need believe the null hypothesis is true! On the contrary, often you suspect there is a relationship between a set of variables. The null hypothesis is used as the basis of an argument because it's possible to test it. So, rejecting a hypothesis does not mean an experiment was "bad" or that it didn't produce results.

To distinguish it from other forms of a hypothesis, the null hypothesis is written ** H_{0}** (which is read as “H-nought”, "H-null", or "H-zero"). A

*significance test*is used to determine the likelihood the results supporting the null hypothesis are not due to chance. A confidence level of 95% or 99% is common. Keep in mind, even if the confidence level is high, there is a chance the null hypothesis is not true, perhaps because the experimenter did not account for a critical factor or due to chance. This is one reason it's important to repeat experiments.

### Examples of the Null Hypothesis

To write a null hypothesis, first start by asking a question.

Rephrase that question in a form that assumes no relationship between the variables. In other words, assume a treatment has no effect.

Question | Null Hypothesis |

Are teens better at math than adults? | Age has no effect on mathematical ability. |

Does taking aspirin reduce your chance of having a heart attack? | Taking low dose aspirin daily does not affect heart attack risk. |

Do teens use a cell phone to access the internet more than adults? | Age has no effect on when a cell phone is used for internet access. |

Do cats care about the color of their food? | Cats express no food preference based on color. |

Does chewing willow bark relieve pain? | There is no difference in pain relief after chewing willow bark versus taking a placebo. |