G

Generalisability (synonyms: applicability, external validity, relevance, transferability)
See external validity.

H

Hazard rate
The probability of an event occurring given that it hasn’t occurred up to the current point in time.

Hazard ratio
A measure of effect produced by a survival analysis. This represents the increased risk with which one group is likely to experience the outcome of interest.  For example, if the hazard ratio for death for a treatment is 0.5, then we can say that treated patients are likely to die at half the rate of untreated patients.

Heterogeneity

1. Used in a general sense to describe the variation in, or diversity of, participants, interventions, and measurement of outcomes across a set of studies, or the variation in internal validity of those studies.
2. Used specifically, as statistical heterogeneity, to describe the degree of variation in the effect estimates from a set of studies. Also used to indicate the presence of variability among studies beyond the amount expected due solely to the play of chance.
   

Heterogeneous
Used to describe a set of studies or participants with sizeable heterogeneity.  The opposite of homogeneous.

Historical control
A control person or group for whom data were collected earlier than for the group being studied. There is a large risk of bias in studies that use historical controls due to systematic differences between the comparison groups, due to changes over time in risks, prognosis, health care, etc.

Homogeneous

1. Used in a general sense to mean that the participants, interventions, and measurement of outcomes are similar across a set of studies.
2. Used specifically to describe the effect estimates from a set of studies where they do not vary more than would be expected by chance.

See also heterogeneity.

Hypothesis
An unproved theory that can be tested through research.  To properly test a hypothesis, it should be pre-specified and clearly articulated, and the study to test it should be designed appropriately.  See also null hypothesis