What is a Hypothesis? - Definition, Lesson & Quiz
A hypothesis is an educated prediction that can be tested. You will discover the purpose of a hypothesis then learn how one is developed and written. Examples are provided to aid your understanding, and there is a quiz to test your knowledge.
Imagine you have a test at school tomorrow. You stay out late and see a movie with friends. You know that when you study the night before, you get good grades. What do you think will happen on tomorrow's test?
When you answered this question you formed a hypothesis! A hypothesis is a specific, testable prediction. It describes in concrete terms what you expect will happen in a certain circumstance. Your hypothesis may have been, 'If not studying lowers test performance, and I do not study, then I will make a low grade on the test'.
The Purpose of a Hypothesis
A hypothesis is used in an experiment to define the relationship between two variables. The purpose of a hypothesis is to find the answer to a question - a formalized hypothesis will force us to think about what results we should look for in an experiment.
The first variable is called the independent variable. This is the part of the experiment that can be changed and tested. The independent variable happens first and can be considered the 'cause' of any changes in the outcome. The outcome is called the dependent variable. The independent variable in our previous example is not studying for a test. The dependent variable that you are using to measure outcome is your test score.
It is important to remember that your hypothesis must be testable. That is, you can perform a test of how two variables might be related. This is what you are doing in a real experiment - you are testing variables. It must also be measurable. If you cannot measure the results, then the information does not help you explain why a particular outcome occurred. Let's use the previous example again to illustrate these ideas. The hypothesis is testable because you will receive a score on your test performance. It is measurable because you can compare test scores received when you did study and test scores received when you did not study.
A hypothesis should always:
- explain what you expect to happen
- be clear and understandable
- be testable
- be measurable
- contain an independent and dependent variable
How to Develop a Hypothesis
Another important aspect of a hypothesis is that it should be based on research. Remember that the purpose of a hypothesis is to find the answer to a question.
The first thing you should do if you want to answer a question is to find as much information on the topic as you can. Before you come up with a specific hypothesis, spend some time doing research. Then, start thinking of questions you still have. After thoroughly researching your question, you should have an educated guess about how things work. This guess about the answer to your question is where your hypothesis comes from.
Let's imagine that you want to know why the leaves on the tree in your front yard change color in the fall. First, you would research this phenomenon. You observe what you see happen and read about the subject. You discover that the color change happens when the temperature cools. What question does this information make you ask?
You come up with the following question: Does temperature cause the leaves to change color on the tree in my front yard? Next, you ask yourself if this can be tested. If it can be tested, you will write a hypothesis that states what you expect to find. Your hypothesis could be, 'If lower temperatures cause leaves to change color, and the temperature surrounding a tree is decreased, then the leaves will change color'.
How to Write a Hypothesis
Let's learn how to properly write a hypothesis using the previous example of tomorrow's test. Examine the differences in the following hypotheses:
Not studying may cause a lower grade on my test.
This statement is not clear enough to be useful. Your hypothesis should be as specific as possible. You are trying to find the answer to a question. If the hypothesis is vague, it is unclear how to find the answer to your question.
If I do not study, then I will make a low grade on the test.
This statement makes a common mistake. You have written a simple cause and effect prediction that is based on an unstated assumption. You are assuming that not studying lowers test performance. You want to minimize these assumptions when you state your hypothesis. A hypothesis is clearer if you state a proposed relationship before making the prediction.
If not studying lowers test performance, and I do not study, then I will make a low grade on the test.
This hypothesis states a proposed relationship between study and test performance. It is worded so that it can be tested, and it makes a clear prediction of what will happen. The statement communicates that if one thing happens, then a second thing will occur.
We've used a couple of examples already, but let's look at some more examples of good vs. poor hypotheses. The following examples will help you better understand how a good hypothesis should look. The better hypothesis will appear in bold.
- If people see funny commercials, then they are more likely to purchase a product.
- If people prefer funny commercials, then funny commercials will produce more sales.
- If you spend a lot of time in the sun, then you will increase your risk of skin cancer.
- If skin cancer is related to sun exposure, then people who spend more time in the sun will have a higher frequency of skin cancer.
- A plant that receives fertilizer will become larger than a plant that does not receive fertilizer.
- If fertilizer helps grow larger plants, and a plant is given fertilizer, then it will be larger than a plant that does not receive fertilizer.
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