# OHDSI — Observational Health Data Sciences and Informatics ## Overview OHDSI (pronounced "Odyssey") is an international, open-science collaborative established in 2014 that generates evidence from observational health data through transparent, reproducible, and multi-database analytics. OHDSI maintains the [[OMOP CDM]] standard, develops the open-source tools that run on it, and coordinates a global network of 500+ data partners covering 700M+ patient records in 30+ countries — enabling large-scale pharmacoepidemiological and outcomes research that no single institution could conduct alone. While [[OMOP CDM]] is the *standard*, OHDSI is the *community and network* that makes it operationally useful. ## What OHDSI Produces ### Open-Source Tools OHDSI develops and maintains the **HADES** (Health Analytics Data-to-Evidence Suite) — a collection of R packages for observational research on OMOP CDM data: | Tool | Purpose | | ---------------------------- | -------------------------------------------------------------------------------------------------------------- | | **ATLAS** | Web-based cohort definition, characterisation, incidence rates, population-level estimation; no-code interface | | **ACHILLES** | Automated data quality and characterisation; generates 170+ statistics on CDM contents | | **CohortDiagnostics** | Diagnose phenotype algorithms across databases | | **FeatureExtraction** | Extract covariates for patient-level prediction and estimation | | **PatientLevelPrediction** | Train and validate ML models for clinical outcomes | | **CohortMethod** | Population-level effect estimation (comparative cohort studies) | | **SelfControlledCaseSeries** | Self-controlled case series analysis | | **Cyclops** | Large-scale regression engine (L1/L2 regularised) | | **DataQualityDashboard** | Systematic data quality assessment against the Kahn framework | | **White Rabbit** | Source data profiling for ETL design | | **Rabbit in a Hat** | Visual ETL mapping tool | ### Network Studies OHDSI coordinates multi-database **network studies** — analytical studies that run identical code across all participating databases, generating site-level results that are meta-analysed centrally. The **OHDSI COVID-19 Studies** (2020) characterised 34,000+ hospitalised patients across 34 databases in 13 countries within 3 weeks of the pandemic. **LEGEND-T2DM** compared the safety of second-line type 2 diabetes treatments across 11 databases and 1.5 million patients. OHDSI also runs neurological disease network studies covering dementia, epilepsy, and Parkinson's disease incidence and treatment patterns. ### Phenotype Library OHDSI maintains an open **Phenotype Library** of validated ATLAS cohort definitions for hundreds of clinical conditions, enabling researchers to reuse rigorously validated phenotype algorithms for disease cohorts. ## OHDSI in France - [[Health Data Hub]] — all SNDS data in the HDH Datalab is OMOP CDM v5.4; ATLAS is the primary analytical interface for HDH users - [[EDS AP-HP]] — [[OMOP CDM]]-based; ATLAS and ACHILLES deployed - French OHDSI community — active participation in OHDSI Europe annual symposia ## Connections - Maintains: [[OMOP CDM]] (the standard) - Adopted by: [[Health Data Hub]], [[EDS AP-HP]], [[ECRIN]], [[BBMRI-ERIC]] - Tools: ATLAS, ACHILLES, HADES R packages, DataQualityDashboard - Vocabularies (via Athena): [[SNOMED CT]], [[LOINC]], [[ICD-10]], [[MedDRA]], [[RxNorm]], [[CCAM]], [[HPO]], [[MONDO]] - Mandated by: [[EHDS]] (OMOP CDM for secondary use) - Working group: [[OHDSI Clinical Trials Working Group]] (SDTM↔OMOP conversion conventions) ## Resources - https://ohdsi.org - https://ohdsi.github.io/Hades/ (HADES R packages documentation) - https://atlas-demo.ohdsi.org (ATLAS public demo instance) - https://athena.ohdsi.org (Athena — OMOP vocabulary browser) - https://www.ohdsi.org/data-standardization/ (CDM and tools overview)