How to write a research hypothesis
A research hypothesis is a clear, testable, falsifiable prediction about the relationship between variables — stated before you collect data. The test that matters: could the data prove it wrong? If not, it isn’t a hypothesis yet. Note up front that hypotheses belong to confirmatory quantitative work — exploratory and qualitative studies use research questions instead.
Null vs alternative
- Null hypothesis (H0) — there is no effect or relationship between the variables.
- Alternative hypothesis (H1) — there is an effect or relationship.
Statistical tests are built around the null: you gather evidence to reject it, or you fail to reject it. You never prove the alternative directly — a subtlety that trips up a lot of discussion sections (see what a p-value actually means).
Directional vs non-directional
A directional (one-tailed) hypothesis predicts the direction — “group A scores higher than group B.” A non-directional (two-tailed) hypothesis predicts a difference or relationship without saying which way. Only go directional when theory or prior evidence genuinely justifies predicting the direction; otherwise two-tailed is the honest default.
Build it from your variables
- Name the variables. Your independent and dependent variables — what you change and what you measure.
- State the expected relationship between them, grounded in theory and the literature.
- Operationalise. Define each variable so it can be measured — a hypothesis about vague constructs can’t be tested.
e.g. “Adults who complete a structured telehealth programme show a greater reduction in HbA1c at three months than those receiving usual care.”
The make-or-break test: is it falsifiable?
A hypothesis that no possible data could contradict is useless. Each one must name measurable variables, predict a specific relationship, and be capable of being wrong. That’s also what makes it testable with a defined statistical test — if you can’t name the test that would evaluate it, the hypothesis isn’t specified tightly enough.
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Frequently asked questions
What is a research hypothesis?
A clear, testable, falsifiable prediction about the relationship between variables, stated before data collection.
Null vs alternative?
The null says there’s no effect; the alternative says there is. Tests reject or fail to reject the null.
Directional vs non-directional?
Directional predicts the direction of the effect; non-directional predicts only a difference. Go directional only when theory justifies it.
Do all studies need a hypothesis?
No — confirmatory quantitative studies do; exploratory and qualitative studies use research questions instead.