How to Write a Hypothesis: Steps and Examples

H1: Patients who receive a nurse navigator discharge program have significantly lower 30-day hospital readmission rates than patients who receive standard discharge planning.

Hypothesis with Mediation

"The relationship between childhood food insecurity and adult depression is mediated by adverse childhood experiences (ACEs): food insecurity increases exposure to ACEs, which in turn increases depression risk in adulthood."

This is a mediation hypothesis. It predicts not just that X relates to Y, but that this relationship operates through a specific mechanism (Z).

Hypothesis vs Research Question vs Thesis Statement

These three terms are often confused:

A research question asks. A hypothesis predicts. A thesis statement argues. Research questions become hypotheses when enough prior evidence exists to support a specific prediction. Thesis statements are for argumentative writing, not empirical research.

Characteristics of a Strong Hypothesis

Testable: The hypothesis can be evaluated with observable data. "Students who study more learn more" is vague. "Students who study for more than two hours per day achieve higher test scores" is testable.

Falsifiable: There must be a result that would prove the hypothesis wrong. If the hypothesis is equally consistent with all possible outcomes, it is not a hypothesis.

Specific: Vague predictions produce vague results. The hypothesis should specify what variables are being compared, in what population, under what conditions.

Grounded: The hypothesis should be derivable from existing theory or prior evidence. State explicitly what evidence or theory supports the prediction.

Concise: A well-formed hypothesis can be stated in one or two sentences. If you need a paragraph to state it, it is probably more than one hypothesis.

Common Mistakes

Stating a fact instead of a prediction. "Students with higher GPAs perform better on standardized tests" is a finding, not a hypothesis. A hypothesis is stated before data collection.

Using "I think" or "I believe." Hypotheses are scientific statements, not personal opinions. Remove first-person hedges.

Non-falsifiable hypothesis. "People's experiences of education are shaped by many factors" cannot be tested or proven wrong. It describes everything and predicts nothing.

Vague variables. "Exercise improves health" has variables too vague to measure. What kind of exercise? What health outcome? Measured how? When?

Hypothesis as question. "Does exercise reduce stress?" is a research question, not a hypothesis. Restate it as a prediction: "Adults who exercise three or more times per week report lower perceived stress than those who do not."

Direction stated without evidence. If you write a directional hypothesis ("X increases Y"), you should cite the prior evidence or theory that supports that direction. A directional prediction without theoretical basis is arbitrary.

Frequently Asked Questions

What is an example of a hypothesis? "Elementary school students who participate in 20 minutes of structured outdoor recess before math class will score higher on in-class math assessments than students who have no recess before math class." This hypothesis identifies the population (elementary students), the manipulation (outdoor recess timing), the outcome (math assessment scores), and the direction of the expected effect.

What is the difference between a hypothesis and a prediction? A prediction is any statement about a future outcome. A hypothesis is a specific type of prediction that is testable, falsifiable, and grounded in theory or prior evidence. All hypotheses are predictions, but not all predictions qualify as scientific hypotheses. "I predict it will rain tomorrow" is a prediction, not a hypothesis.

How do you write a null hypothesis? A null hypothesis states that there is no relationship between the variables being studied. Write it as the direct negation of your alternative hypothesis. If H1 is "Students who receive feedback perform better than those who do not," H0 is "There is no significant difference in performance between students who receive feedback and those who do not." The null hypothesis is what statistical tests are designed to evaluate.

Should a hypothesis be a statement or a question? A hypothesis is always a statement, not a question. The question form is the research question. The hypothesis answers the research question with a specific prediction. "Does caffeine improve memory?" is a research question. "Caffeine consumption of 200mg improves short-term memory recall compared to placebo" is a hypothesis.

How is a hypothesis different from a theory? A hypothesis is a specific, testable prediction about a single study. A theory is a broader, well-supported framework that explains a pattern of findings across many studies. Hypotheses are tested in individual studies. Theories are built up from many replicated findings. A good hypothesis is derived from theory, but a single confirmed hypothesis does not validate a theory.

For related research writing guidance, see research question examples and how to write a research paper introduction.