hypothesis

A hypothesis is a tentative explanation or educated guess that can be tested by experiments and observations. In science, it is a specific, testable statement about a relationship between variables, designed to be falsifiable. Hypotheses guide study design, data collection, and analysis.

The word hypothesis derives from the Greek hypo- meaning under and thesis meaning placing, reflecting the idea of placing a proposed explanation under test.

There are two main statistical hypotheses: the null hypothesis (H0), which states there is no effect or relationship, and the alternative hypothesis (Ha or H1), which asserts an effect or relationship. Hypotheses can be directional (one-tailed) or non-directional (two-tailed), and they may be simple or composite.

Formulation and testing: A good hypothesis is testable and operationalizable into measurable variables. Researchers collect data to determine whether the results are consistent with H0. Statistical tests produce a p-value; if p < alpha, H0 is rejected in favor of Ha. If not, H0 is not rejected.

Relationship to theory and limitations: Hypotheses originate in existing theory and prior observations and contribute to theory testing rather than proving; they are falsifiable. Limitations include bias, measurement error, sample size, and multiple testing; preregistration and replication improve reliability.

Example: If a plant receives more sunlight, its growth rate increases. H0: sunlight has no effect on growth rate.