A hypothesis is a statement about some real-world phenomenon that can be tested through observations.[1] It is a proposition that suggests that one thing will result in some effect on or change in another. Put more formally, it is an argument that change in one variable will result in some change in another.[2] Many academic fields, from the physical sciences to social sciences, use hypothesis testing as a means of learning about the world and advancing knowledge. Whether you are a beginning scholar or just a student taking a class in one of these subjects, understanding hypotheses and being able to generate them yourself will be very important. These instructions will help get you started.
Steps
Preparing to Write a Hypothesis
- Select a topic. Pick a topic that interests you, and that you think it would be good to know more about.[3]
- If you are writing a hypothesis for a school assignment, this step may be taken care of for you.
- Gather the literature. Gather all the information you can about the topic you've selected. You'll need to become an expert on the subject and develop a good grasp of what is already known about the topic.[4]
- Focus on academic and scholarly writing. You need to be certain that your information is unbiased, accurate, and comprehensive.
- You can find information in textbooks, at a library, and online. If you are in school, you can also ask for help from teachers, librarians, and your peers.
- Analyze the literature. Spend some time reading the materials you've collected. As you do so, look for and make note of unanswered questions in the literature. These can provide excellent ideas for areas to investigate.
- For example, if you are interested in the effects of caffeine on the human body, but notice that nobody seems to have explored whether caffeine affects men differently than it does women, this could be something to formulate a hypothesis about. Or, if you are interested in organic farming, you might notice that no one has tested whether organic fertilizer results in different growth rates for plants than chemical fertilizer.
- You can sometimes find holes in the existing literature by looking for statements like “it is unknown” or places where information is clearly missing.
- Examining these types of questions provides an excellent way for you to set yourself apart by filling in important gaps in a field of study.
- Generate questions. After studying the literature on your topic, generate one or more unanswered questions you'd be interested in exploring further. These are your research questions.[5]
- Following the examples above, you might ask: "does caffeine affect women differently than men?" or "does organic fertilizer affect plant growth differently than chemical fertilizer?" The rest of your research will be aimed at answering these questions.
- Look for clues as to what the answer might be. Once you've generated your research question or questions, look to see if the existing findings and/or theories about the topic provide any clues that would allow you to make an educated guess as to what the answers to your research questions might be.[6] If so, this will form the basis for your hypothesis.
- Following the examples above, if you found out that some other types of stimulants seem to affect women more than men, this could be a clue that the same might be true for caffeine. Similarly, if you found that organic fertilizer resulted in smaller plants overall, you might guess that it might also lead to slower growth.
Formulating Your Hypothesis
- Determine your variables. A hypothesis must state a relationship you think may exist between two variables: and independent variable and a dependent variable.
- You can think of the independent variable as the one that is causing some kind of difference or effect to occur. In the examples, the independent variable would be sex, i.e. whether a person is male or female, and fertilizer type, i.e. whether the fertilizer is organic or chemical-based.
- The dependent variable is what is affected by (i.e. "depends" on) the independent variable. In the examples above, the dependent variable would be the impact of caffeine or fertilizer.
- Your hypothesis should only suggest one relationship. Most importantly, it should only have one independent variable. If you have more than one, you won't be able to determine which one is actually the source of any effects you might observe.[7]
- Generate a general hypothesis. Once you've spent some time thinking about your research question and variables, write down your initial idea about how the variables might be related as a simple declarative statement.[8]
- Don't worry too much at this point about being precise or detailed.
- In the examples above, one hypothesis would make a statement about whether a person's sex might impact the way they are affected by caffeine; for example, at this point, your hypothesis might simply be: "men and women will be affected differently by caffeine." The other hypothesis would make a general statement about plant growth and fertilizer; for example your general hypothesis might be "plants given different types of fertilizer will grow at different rates."
- Decide on direction. Hypotheses can either be directional or non-directional. A non-directional hypothesis simply says that one variable will affect the other in some way, but doesn't say specifically how.[9] A directional hypothesis provides more information about the nature (or "direction") of the relationship, stating specifically how one variable will affect the other.[10]
- Using our example, our non-directional hypotheses would be "there is a relationship between a person's sex and how much caffeine increases their heart rate," and "there is a relationship between fertilizer type and the speed at which plants grow."
- Directional hypotheses using the same examples would be : "women will experience a greater increase in heart rate after consuming caffeine than will men," and "plants fertilized with chemical fertilizer will grow faster than those fertilized with organic fertilizer."
- If the literature provides any basis for making a directional hypothesis, it is better to do so, because it provides more information. Especially in the physical sciences, non-directional hypotheses are often seen as inadequate.[11]
- Get specific. Once you've got an initial idea on paper, it's time to start refining. Make your hypothesis as specific as you can, so it's clear exactly what ideas you will be testing and what would provide evidence of a relationship between the variables.
- Where necessary, specify the population (i.e. the people or things) you hope to uncover new knowledge about.[12] For example, if you were only interested the effects of caffeine on elderly people, your hypothesis might read: "women over the age of 65 will experience a greater increase in heart rate than will men of the same age." If you were interested only in how fertilizer affects tomato plants, your hypothesis might read: "tomato plants treated with chemical fertilizer will grow faster in the first three months than will tomato plants treated with organic fertilizer."
- Make sure it is testable. Your hypothesis must suggest a relationship between two variables that can feasibly be observed and measured in the real world. If it doesn't, it's time to go back to the drawing board.[13]
- For example, you would not want to make the hypothesis: "older people think differently." This hypothesis does not specify who counts as "older," who they are supposed to think differently than, or how would know whether or not their thoughts were "different." As a result, this hypothesis cannot be supported or rejected based on real world observations. There is no way to observe "different" thoughts, even if we knew who's thoughts we were comparing them with.
- State your hypothesis formally. Now it's time to write down the final version of your hypothesis. It should clearly state the proposed relationship between your independent and dependent variables, and be numbered according to scientific conventions.
- Hypotheses are denoted by the letter "H" and a number, followed by a colon. In a research project with multiple hypotheses, each should have a different number.[14]
- Using the first example, you'd write down: "H1: Women over the age of 65 will experience a greater increase in heart rate after consuming a can of caffeinated soda than will men of the same age." Later in your research report, you might have another hypothesis, "H2: Women over the age of 65 will experience a greater increase in perspiration after consuming a can caffeinated soda than will men of the same age." Using the second example, you'd write down: "H1: Tomato plants treated with chemical fertilizer will grow faster in the first three months than will tomato plants treated with organic fertilizer." Later in the report, you might have second hypothesis, "H2: Corn plants treated with chemical fertilizer will grow faster in the first three months than will tomato plants treated with organic fertilizer."
- Often, but not always, hypotheses are stated in the form of if-then sentences. For example, "if children are given caffeine, then their heart rates will increase."
- Create your null hypothesis or hypotheses. Next, you'll need to determine what evidence would suggest your hypothesis is wrong, and state it in hypothesis form. This is called your null hypothesis.[15]
- It may sound strange, but researchers don't ever prove that a hypothesis is right or wrong. Instead, they look for evidence that the opposite of their hypotheses is probably not true. If the opposite is probably not true, the hypothesis probably is true.[16]
- Using the examples, if you were to test the effects of caffeine on the heart rates of both men and women, evidence that H1 is not true could occur if men's heart rates were affected more than women's, or if there was no difference between men and women at all. If you wanted to test the effects of different fertilizer types, evidence that your hypothesis was not true would be the plants grew at the same rate, regardless of fertilizer, or if plants treated with organic fertilizer grew faster.
- A null hypothesis is denoted by the letter "H" and the number 0, followed by a colon. Lowercase letters can be used to distinguish between null hypotheses if there are more than one.[17]
- For example: "H0a: Men over the age of 65 will experience a greater increase in heart rate after consuming a can caffeinated soda than will women of the same age," and "H0b: Among people over the age of 65, the heart rates of men and women will be impacted equally by the consumption of a can of caffeinated soda." Or, using the second example: "H0a: Tomato plants treated with organic fertilizer will grow faster in the first three months than will tomato plants treated with chemical fertilizer," and "H0b: Tomato plants treated with organic fertilizer will grow at the same rate during the first three months as tomato plants treated with chemical fertilizer.
- Test your hypothesis. Make your observations or conduct your experiment. Hopefully, your evidence will allow you to reject your null hypotheses, thus lending support to your research hypothesis.
Tips
- Don't reinvent the wheel. When examining the literature, look for research that is similar to what you want to do, and try to build on the findings of other researchers.
- Be specific in your hypotheses, but not so specific that your hypothesis can't be applied to anything outside your specific experiment.[18] You definitely want to be clear about the population you are interested in drawing conclusions about, but nobody will be interested in reading a paper with the hypothesis: "my three roommates will each be able to do a different amount of pushups."
- Keep your feelings and opinions out of your research. Hypotheses aren't about you, and your hypothesis should never say "I believe," "I think," or "I feel."[19]
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Sources and Citations
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