A hypothesis is a prediction of the outcome of a test. It forms the basis for designing an experiment in the scientific method. A good hypothesis is testable, meaning it makes a prediction you can check with observation or experimentation. Here are different hypothesis examples.

### Null Hypothesis Examples

The null hypothesis (H_{0}) is also known as the zero-difference or no-difference hypothesis. It predicts that changing one variable (independent variable) will have no effect on the variable being measured (dependent variable). Here are null hypothesis examples:

- Plant growth is unaffected by temperature.
- If you increase temperature, then solubility of salt will increase.
- Incidence of skin cancer is unrelated to ultraviolet light exposure.
- All brands of light bulb last equally long.
- Cats have no preference for the color of cat food.
- All daisies have the same number of petals.

Sometimes the null hypothesis shows there is a suspected correlation between two variables. For example, if you think plant growth is affected by temperature, you state the null hypothesis: “Plant growth is not affected by temperature.” Why do you do this, rather than say “If you change temperature, plant growth will be affected”? The answer is because it’s easier applying a statistical test that shows, with a high level of confidence, a null hypothesis is correct or incorrect.

### Research Hypothesis Examples

A research hypothesis (H_{1}) is a type of hypothesis used to design an experiment. This type of hypothesis is often written as an if-then statement because it’s easy identifying the independent and dependent variables and seeing how one affects the other. If-then statements explore cause and effect. In other cases, the hypothesis shows a correlation between two variables. Here are some research hypothesis examples:

- If you leave the lights on, then it takes longer for people to fall asleep.
- If you refrigerate apples, they last longer before going bad.
- If you keep the curtains closed, then you need less electricity to heat or cool the house (the electric bill is lower).
- If you leave a bucket of water uncovered, then it evaporates more quickly.
- Goldfish lose their color if they are not exposed to light.
- Workers who take vacations are more productive than those who never take time off.

### Is It Okay to Disprove a Hypothesis?

Yes! You may even choose to write your hypothesis in such a way that it can be disproved because it’s easier to prove a statement is wrong than to prove it is right. In other cases, if your prediction is incorrect, that doesn’t mean the science is bad. Revising a hypothesis is common. It demonstrates you learned something you did not know before you conducted the experiment.

Test yourself with a Scientific Method Quiz.

### References

- Mellenbergh, G.J. (2008). Chapter 8: Research designs: Testing of research hypotheses. In H.J. Adèr & G.J. Mellenbergh (eds.),
*Advising on Research Methods: A Consultant’s Companion*. Huizen, The Netherlands: Johannes van Kessel Publishing. - Popper, Karl R. (1959).
*The Logic of Scientific Discovery*. Hutchinson & Co. ISBN 3-1614-8410-X. - Schick, Theodore; Vaughn, Lewis (2002).
*How to think about weird things: critical thinking for a New Age*. Boston: McGraw-Hill Higher Education. ISBN 0-7674-2048-9. - Tobi, Hilde; Kampen, Jarl K. (2018). “Research design: the methodology for interdisciplinary research framework”.
*Quality & Quantity*. 52 (3): 1209–1225. doi:10.1007/s11135-017-0513-8