Term<\/strong><\/td>Definition<\/strong><\/td><\/tr><\/thead>Cohort<\/strong><\/td>| A group of individuals sharing a common characteristic or exposure who are followed together over time<\/td><\/tr> | Exposure<\/strong><\/td>| Any factor\u2014biological, chemical, behavioural, or environmental\u2014whose association with a health outcome is being investigated (e.g., smoking, a drug, a toxin)<\/td><\/tr> | Outcome<\/strong><\/td>| The health event or endpoint being measured, such as disease diagnosis, death, or change in health status<\/td><\/tr> | Prospective Cohort Study<\/strong><\/td>| A cohort study that follows participants forward in time from exposure assessment to outcome occurrence<\/td><\/tr> | Retrospective Cohort Study<\/a><\/strong><\/td>| A cohort study in which both exposure and outcome have already occurred; historical records are used to reconstruct the study<\/td><\/tr> | Incidence<\/a><\/strong><\/td>The number of new<\/em> cases of a disease or outcome arising in a population over a defined time period<\/td><\/tr>Prevalence<\/a><\/strong><\/td>| The proportion of a population that has a disease or condition at a single point in time<\/td><\/tr> | Cumulative Incidence (Risk)<\/strong><\/td>| The proportion of individuals in a cohort who develop the outcome over the entire follow-up period<\/td><\/tr> | Incidence Rate (Incidence Density)<\/strong><\/td>| The number of new cases divided by total person-time at risk; reflects the speed at which new cases occur<\/td><\/tr> | Person-Time<\/strong><\/td>| The sum of the time each individual participant contributed to the study while free of the outcome; used as the denominator in incidence rate calculations<\/td><\/tr> | Risk Ratio (Relative Risk)<\/strong><\/td>| The ratio of the risk of the outcome in the exposed group to the risk in the unexposed group; a value >1 indicates increased risk<\/td><\/tr> | Risk Difference (Attributable Risk)<\/strong><\/td>| The absolute difference in incidence between the exposed and unexposed groups; reflects the excess risk attributable to the exposure<\/td><\/tr> | Confounding<\/strong><\/td>| Distortion of the exposure\u2013outcome relationship by a third variable that is associated with both the exposure and the outcome (e.g., age, sex)<\/td><\/tr> | Attrition Bias<\/strong><\/td>| Systematic error introduced when participants who drop out of a study differ in meaningful ways from those who remain<\/td><\/tr> | Recall Bias<\/strong><\/td>| Error that arises when participants’ recollection of past exposures is influenced by their current disease status; less of a concern in prospective cohort studies<\/td><\/tr> | Loss to Follow-Up<\/strong><\/td>| The failure to collect outcome data on participants who leave or disengage from a study before it concludes<\/td><\/tr> | Temporality<\/strong><\/td>| The requirement that exposure must precede outcome in time; a key criterion for establishing causality and a strength of prospective cohort designs<\/td><\/tr> | Nested Case-Control Study<\/strong><\/td>A case-control study <\/a>conducted within an existing defined cohort, drawing both cases and controls from the same cohort population<\/td><\/tr>STROBE<\/strong><\/td>| Strengthening the Reporting of Observational Studies in Epidemiology\u2014an international checklist of standards for reporting observational studies including cohort studies<\/td><\/tr> | CASP<\/strong><\/td>| Critical Appraisal Skills Programme\u2014provides structured checklists for evaluating the methodological quality of research studies, including cohort studies<\/td><\/tr> | Baseline<\/strong><\/td>| The starting point of a cohort study, at which participants are enrolled, exposure is assessed, and all members are confirmed free of the outcome of interest<\/td><\/tr> | Open (Dynamic) Cohort<\/strong><\/td>| A cohort in which new participants can enter and others can leave throughout the study period<\/td><\/tr> | Closed Cohort<\/strong><\/td>| A cohort in which all participants are fixed at the outset; no new members are added during follow-up<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n | | | | | | | | | | | | | | | | | | | | | | | | | | | |