If the first group had a risk ratio of 2, subjects in that group would be twice as likely to have the event happen. A risk ratio of less than 1 means the outcome is less likely in the first group. The risk ratio is sometimes referred to as relative risk. Secondary outcome An outcome used to evaluate additional effects of the intervention deemed a priori as being less important than the primary outcomes. Selection bias Selection bias occurs if: a) The characteristics of the people selected for a study differ from the wider population from which they have been drawn, or b) There are differences between groups of participants in a study in terms of how likely they are to get better. Sensitivity How well a test detects the thing it is testing for. If a diagnostic test for a disease has high sensitivity, it is likely to pick up all cases of the disease in people who have it (that is, give a true positive result). But if a test is too sensitive it will sometimes also give a positive result in people who don t have the disease (that is, give a false positive ). For example, if a test were developed to detect if a woman is 6 months Chronic Heart Failure Glossary NICE 2018. All rights reserved. Subject to Notice of rights. ISBN: 978-1-4731-3093-7 Term Definition pregnant, a very sensitive test would detect everyone who was 6 months pregnant, but would probably also include those who are 5 and 7 months pregnant. If the same test were more specific (sometimes referred to as having higher specificity), it would detect only those who are 6 months pregnant, and someone who was 5 months pregnant would get a negative result (a true negative ). 