The Three Steps to Writing a Good Hypothesis

Remember that there is no single and magical scientific method. What matters, is that you may not know the results of an experiment, but you can make a reasonable prediction to find a verifiable answer. In real experiments, real hypotheses should be written before the actual experiment.

One of the most important (and one of the trickiest) skills a scientist has is his/her ability to write a good hypothesis.  A hypothesis for a project, a paper or an experiment is key to guiding you in the right direction as you reach your conclusion. A good hypothesis is the result of research and refinement and has a few key characteristics that make it helpful, understandable and provable.

A refined hypothesis isn't an educated guess. It is a tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation. Your final hypothesis should look like you are stating the obvious - it is obvious only because of your research.  You haven't actually done the experiment.  Now it's time to run the experiment to prove the hypothesis. Once you do the experiment and prove the hypothesis, it becomes part of scientific theory.

The best way to develop a hypothesis is in a three-step process. This will help you to narrow things down, and is the most foolproof method to correctly achieve a testable hypothesis.

The Three Step Process

The general hypothesis states the general relationship between the major variables.
The directional hypothesis refines the general hypothesis by stating the direction of the difference or relationship.

The measurable hypothesis finalizes the direction in more specific terms and uses the correct If...then...because format. It avoids using words like I, think, believe, all, never, and sometimes because these words may either personalize it or are too vague and will result in too broad of an area to research.

Example 1:
Anne has noticed that 8th grade girls seem to get better grades on organizational skills tests such as notebook quizzes.

Anne writes a general hypothesis which states:

"Boys and girls receive different grades on organizational skills tests."

Do you notice how general this hypothesis is? Do you see that it does not state the direction of the difference?

Anne later writes a directional hypothesis which states:

"Girls get better grades than boys on tests of organizational abilities."

Do you see that she has now given a direction of the relationship, i.e. girls do better than boys? However, this hypothesis is not measurable in its current form.

Anne finally writes a measurable hypothesis in the correct If...then...because format.
The measurable hypothesis states:

"If eighth grades girls take written quizzes, then they will receive significantly higher grades than eighth grade boys because eighth grade girls have better writing skills."

Do you see that Anne has added specific details that make the hypothesis measureable? What difference will you measure? The difference in scores on written quizzes between 8th grade boys and 8th grade girls. You should also see that the hypothesis is specific to 8th graders.

Example 2:

A worker on a fish-farm notices that his trout seem to have more fish lice in the summer, when the water levels are low, and wants to find out why. His research leads him to believe that the amount of oxygen is the reason - fish that are oxygen stressed tend to be more susceptible to disease and parasites.
He proposes a general hypothesis.

“Water levels affect the amount of lice suffered by rainbow trout.”

This is a good general hypothesis, but it gives no guide to how to design the research or experiment. The hypothesis must be refined to give a little direction.

He later writes a directional hypothesis which states:

“Rainbow trout suffer more lice when water levels are low.”

Now there is some directionality, but the hypothesis is not really testable, so the final stage is to design an experiment around which research can be designed, a testable hypothesis.

The researcher finally writes a measurable hypothesis in the correct If… then…because format.

The measurable hypothesis states:

“If water levels are low then Rainbow trout will suffer more lice because there is less oxygen in the water.”

This is a testable hypothesis – the researcher has established variables, and by measuring the amount of oxygen in the water, eliminating other controlled variables, such as temperature, he/she can see if there is a correlation against the number of lice on the fish.

This is an example of how a gradual focusing of research helps to define how to write a hypothesis.

So how should you write a hypothesis?

Now you are ready to write a hypothesis.

  1. Start by stating the general hypothesis in a simple declarative statement.
  2. Do not use the terms "I think" to start the hypothesis.
  3. Now that you have written the general hypothesis, write the directional hypothesis.
  4. With the directional hypothesis behind you, finish with the measureable hypothesis.