Hazard Ratio
Definition
The ratio of the rate at which an event occurs in the treatment arm to the rate in the control arm over time. Below 1 favours treatment, and an interval crossing 1 has not demonstrated a difference.
What this means for research sourcing
Understanding evidence quality helps researchers prioritize compounds. Volta's research library summarizes the literature behind stocked compounds.
Related Terms in Evidence & Research
Sample Size
How many participants a study enrolled, written as n. Small samples give unstable estimates and are the commonest reason an early positive result fails to replicate.
Pilot Study
A small preliminary study run to test feasibility and gather estimates for designing a real one. Pilot results are routinely over-read as findings in their own right, which they are not.
Case Report and Case Series
A published description of one patient, or a handful, with no control group. Useful for flagging a rare harm or an unexpected observation, and not evidence that something works.
Observational Study
Research that records what happens without assigning the intervention, in cohort or case-control form. It shows association at a scale trials cannot reach and can never rule out that the groups differed to begin with.
Systematic Review
A review that follows a search and appraisal protocol written in advance, so which studies were included is reproducible rather than left to the author's discretion.
Meta-Analysis
Statistical pooling of results from several studies into one estimate. Its reliability is capped by the quality of what it pools and by which studies were published in the first place, so a pooled figure is not automatically a better one.
Cochrane Review
A systematic review published by Cochrane, an international network with published methodology and conflict-of-interest rules. Cochrane reviews are generally treated as among the more rigorous syntheses available.
Publication Bias
The tendency for positive results to be published while null and negative ones are not, which leaves the visible literature skewed toward effects. In a field with few large trials it is the single largest distortion.