hypothesis
Meaning of hypothesis: A study is built backward from it: the question decides the design, the number of participants, and what will count as an answer.
Definition of hypothesis
A hypothesis is a proposed explanation for an observation or a pattern of findings, offered as a starting point for investigation rather than as a settled conclusion. To be useful it has to be framed so that observation, experiment or study could contradict it. A proposal that no possible result would count against is not a testable hypothesis.
How does a hypothesis shape a study?
Stating the hypothesis before any data are collected is what makes a study interpretable afterward. It fixes what is being compared, in whom, and by which measure, so the reported result cannot be chosen after the fact from whatever the data happened to show. Everything else follows from it: the design, the number of participants needed to detect an effect of a given size, and the single main outcome the study exists to answer. Findings that turn up outside the stated question are treated as observations to be tested later rather than as conclusions, because the more comparisons made within one dataset, the more likely it becomes that one looks striking through chance alone. A single-blind study and other design choices protect the same thing: an answer that expectation has not quietly shaped.
What are the null and alternative hypotheses?
| Null hypothesis | Alternative hypothesis | |
|---|---|---|
| What it states | There is no difference, or no effect | There is a difference, or an effect |
| Role in the analysis | The position tested against the data | What is accepted if the null is rejected |
| Possible outcomes | Rejected, or not rejected | Supported, or not supported |
The asymmetry matters. Statistical testing can produce evidence against the null hypothesis, but failing to find that evidence is not the same as showing the null is true. A study too small to detect a real effect returns the same verdict as a study of an effect that does not exist, which is why the size of a study and the width of its confidence interval are read alongside any conclusion drawn from it.
How is it different from a theory?
In everyday speech a theory is a guess, which is close to the opposite of the scientific meaning. A scientific theory is an explanation that has already survived repeated attempts to contradict it and that accounts for many separate lines of evidence. A hypothesis is the tentative starting point before any of that has occurred. Between the two sit the graded levels of evidence used in medicine to describe how much support a claim has accumulated, running from a single small study up to consistent findings across large randomized trials. Climbing that scale is what converts a hypothesis into established knowledge, and one study rarely completes the climb by itself.
Used in a sentence
The study was designed to test the hypothesis that the new approach would improve patient outcomes.
Good to know
A hypothesis is a tentative, testable proposal, while a scientific theory reflects an explanation already supported by a substantial body of evidence, a distinction often blurred in everyday use of the word theory.
Word origin
Where “hypothesis” comes from
Formed from hypo-, Greek for under, and thesis, meaning a placing or proposition, together suggesting a proposition put forward for consideration.