Step 5: Hypothesis Statement
(will be worked on in class prior to due date)
Your hypothesis statement will be turned in during science class, reviewed by the teacher and returned. Below is a short explanation of a hypothesis statement and some examples of hypothesis statements.
Hypothesis statement--a prediction that can be tested or an educated guess.
In a hypothesis statement, students make a prediction about what they think will happen or is happening in their experiment. They try to answer their question or problem.
Question: Why do leaves change colors in the fall?
Hypothesis: I think that leaves change colors in the fall because they are not being exposed to as much sunlight.
Hypothesis: Bacterial growth may be affected by temperature.
Hypothesis: Chocolate may cause pimples
All of these are examples of hypotheses because they use the tentative word "may." However, their form in not particularly useful. Using the word does not suggest how you would go about proving it. If these statements had not been written carefully, they may not have been a hypotheses at all.
A better way to write a hypotheses is to use a formalized hypotheses
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.
Example: If leaf color change is related to temperature, then exposing plants to low temperatures will result in changes in leaf color.
Example: If the rate of photosynthesis is related to wave lengths of light, then exposing a plant to different colors of light will produce different amounts of oxygen.
Example: If the volume of a gas is related to temperature, then increasing the temperature will increase the volume.
These examples contain the words, if and then. Formalized hypotheses contain two variables. One is "independent" and the other is "dependent." The independent variable is the one you, the scientist control and the dependent variable is the one that you observe and/or measure the results.
The ultimate value of a formalized hypotheses is it forces us to think about what results we should look for in an experiment.
Example: If the diffusion rate (dependent variable) through a membrane is related to molecular size (independent variable), then the smaller the molecule the faster it will pass through the membrane.
A scientific hypothesis is the initial building block in the scientific method. Many describe it as an "educated guess," based on prior knowledge and observation. While this is true, the definition can be expanded. A hypothesis also includes an explanation of why the guess may be correct, according to National Science Teachers Association.
A hypothesis is a suggested solution for an unexplained occurrence that does not fit into current accepted scientific theory. The basic idea of a hypothesis is that there is no pre-determined outcome. For a hypothesis to be termed a scientific hypothesis, it has to be something that can be supported or refuted through carefully crafted experimentation or observation. This is called falsifiability and testability, an idea that was advanced in the mid-20th century a British philosopher named Karl Popper, according to the Encyclopedia Britannica.
A key function in this step in the scientific method is deriving predictions from the hypotheses about the results of future experiments, and then performing those experiments to see whether they support the predictions.
A hypothesis is usually written in the form of an if/then statement, according to the University of California. This statement gives a possibility (if) and explains what may happen because of the possibility (then). The statement could also include "may."
Here are some examples of hypothesis statements:
- If garlic repels fleas, then a dog that is given garlic every day will not get fleas.
- Bacterial growth may be affected by moisture levels in the air.
- If sugar causes cavities, then people who eat a lot of candy may be more prone to cavities.
- If UV light can damage the eyes, then maybe UV light is a cause of blindness.
Testing a hypothesis
Notice that all of the statements, above, are testable. The primary trait of a hypothesis is that something can be tested and that those tests can be replicated, according to Midwestern State University.
An example of untestable statement is, "All people fall in love at least once." The definition of love is subjective. Also, it would be impossible to poll every human about their love life. An untestable statement can be reworded to make it testable, though. For example, the previous statement could be changed to, "If love is an important emotion, some may believe that everyone should fall in love at least once." With this statement, the researcher can poll a group of people to see how many believe people should fall in love at least once.
A hypothesis is often examined by multiple scientists to ensure the integrity and veracity of the experiment. This process can take years, and in many cases hypotheses do not go any further in the scientific method as it is difficult to gather sufficient supporting evidence.
"As a field biologist my favorite part of the scientific method is being in the field collecting the data," Jaime Tanner, a professor of biology at Marlboro College, told Live Science. "But what really makes that fun is knowing that you are trying to answer an interesting question, so the first step in identifying questions and generating possible answers (hypotheses) is also very important and is a creative process. Then once you collect the data you analyze it to see if your hypothesis is supported or not."
A null hypothesis is the name given to a hypothesis that is possibly false or has no effect. Often, during a test, the scientist will study another branch of the idea that may work, which is called an alternative hypothesis, according to the University of California, Berkeley.
During a test, the scientist may try to prove or disprove just the null hypothesis or test both the null and the alternative hypothesis. If a hypothesis specifies a certain direction, it is called one-tailed hypothesis. This means that the scientist believes that the outcome will be either with effect or without effect. When a hypothesis is created with no prediction to the outcome, it is called a two-tailed hypothesis because there are two possible outcomes. The outcome could be with effect or without effect, but until the testing is complete, there is no way of knowing which outcome it will be, according to the Web Center for Social Research Methods.
During testing, a scientist may come upon two types of errors. A Type I error is when the null hypothesis is rejected when it is true. A Type II error occurs when the null hypothesis is not rejected when it is false, according to the University of California, Berkeley.
Upon analysis of the results, a hypothesis can be rejected or modified, but it can never be proven to be correct 100 percent of the time. For example, relativity has been tested many times, so it is generally accepted as true, but there could be an instance, which has not been encountered, where it is not true. For example, a scientist can form a hypothesis that a certain type of tomato is red. During research, the scientist then finds that each tomato of this type is red. Though his findings confirm his hypothesis, there may be a tomato of that type somewhere in the world that isn't red. Thus, his hypothesis is true, but it may not be true 100 percent of the time.
The evolution of a hypothesis
Most formal hypotheses consist of concepts that can be connected and their relationships tested. A group of hypotheses comes together to form a conceptual framework. As sufficient data and evidence are gathered to support a hypothesis, it becomes a working hypothesis, which is a milestone on the way to becoming a theory. Though hypotheses and theories are often confused, theories are the result of a tested hypothesis. While hypotheses are ideas, theories explain the findings of the testing of those ideas.
"Theories are the ways that we make sense of what we observe in the natural world. Theories are structures of ideas that explain and interpret facts," said Tanner.