Standardization: method for removing the effect of potential confounders such as age, gender, race from risk estimations.

Standardized incidence rate (SIR): the ratio of incident cases observed in the study group or population in a time period to the number of expected deaths if the study population has the mortality experience of the standard population.

Standardized mortality rate (SMR): the ratio of deaths observed in the study group or population in a time period to the number of expected deaths if the study population has the mortality experience of the standard population.

Standby mode: nuclear facilities available for operation but not currently operating.

Statistical power: the probability that a test will reject a null hypothesis when the hypothesis is actually false.

Statistical significance: refers to a result that is unlikely to be caused by chance; see “P (probability) value.”

Stratification: the process of separating a sample into categories according to a specific criterion, e.g., age, gender, smoking status.

Susceptibility: the risk of becoming afflicted by something that can impact health.

Temporality: the issue associated with specific study designs (e.g., cross-sectional studies, case-control studies) that makes it difficult to understand if exposure or disease came first.

Uncertainty: Lack of sureness or confidence in predictions of models or results of measurements (NCRP Report No. 158).