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Data Dictionary

The Data Dictionary is a document that reviews and explains every OHCAO data variable. This document is designed to be a helpful reference tool for participating agencies. In the data dictionary each variable is defined, the source is cited, and coding examples are provided.

Originally, the OHCAO dataset and dictionary were developed by a committee made up of experienced leaders and stakeholders in the field of emergency medcine, in consultation with individual ambulance services. Since that time, OHCAO staff have continued to update and refine the OHCAO dataset and dictionary based on feedback from ambulance services and relevant findings in the OHCA literature.

The sources that were used for the development of the dataset and dictionary include the Paper Record Form (PRF) and the Utstein template.

PRF is designed to show all stages of care given to the patient by first responders, Doctors and ambulance crews. Paper PRF is made up of two self-carbonising sheets; the top copy is retained on station for monthly checks and then sent to the appropriate Audit department; the bottome copy accompanies the patient.
Utstein is the recognised international standard for reporting out-of-hospital cardiac arrest survival. The Utstein style was first proposed for emergency medical services in 1991. The Utstein recommendations are an attempt to develop and present consensus definitions for previously poorly defined areas of clinical epidemiology as they pertain to OHCA patients.1
The data dictionary is reviewed by the OHCAO project team annually. Please contact the team at ohcao at warwick dot ac dot uk with any questions or comments regarding this document.

1 Jacobs et al. (2004), 110, 3385-3397

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Data Elements:

The data submitted to the OHCAO registry consists of a set of core variables and supplementary variables. The core variable selection was informed by the Utstein recommendations for OHCA reporting and capture case mix, structure process and outcomes. The OHCAO Core Variables are those that are collected and provided by all ambulance service trusts.

There are also Supplementary Variables that are submitted to the OHCAO registry. These are not collected by all ambulance services.

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Ethics and Governance:

Research Ethics

We have carefully considered the data that are required to examine the epidemiology and outcome of OHCA. Ethics committee permissions were gained from South Central—Oxford C Research Ethics Committee (reference 13/SC/0361). The study has also received approval from the Confidentiality Advisory Group (CAG) Ethics and Confidentiality committee (ECC 8-04(C)/2013), which provides authorisation, on behalf of the Secretary of State, to lawfully hold identifiable data on patients without their consent . We will comply with the common law duty of confidentiality owed by health professionals in regard to information provided by patients in the course of clinical care, and the principles of the Data Protection Act 1998, which apply to the processing of data by Research Databases in the same way as to specific research projects. The project has received approval from the CAG for permission to implement Section 251 of the NHS Act 2006 (originally enacted under Section 60 of the Health and Social Care Act 2001), which allows identifiable patient information to be used without consent in very specific circumstances. The CAG approval also provides the Steering Committee with the authority to provide other researchers access to anonymised data in specific circumstances.

Research Governance

All members working on the project have completed Information Governance training and the project has achieved a satisfactory achievement standard for 2014 for the Information Governance Toolkit Assessment. All staff follow the University of Warwick's policy on data protection.

Confidentiality Advisory Group (formerly National Information Governance Board) approval April 2013, reference number ECC 8-04(c)/2013: CAG Advice and HRA/SofS Approval Decisions)

ISRCTN registry ISRCTN10428536

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Quality Assurance:

The OHCAO quality assurance process process consists of a number of measures that are taken to ensure the integrity and cleanliness of the data. These measures include training for all OHCAO team members and ambulance service personnel, built-in software logic, an automated audit algorithm ensuring data validation across the entire registry, and assessment of data quality.


Each member of the OHCAO project team are familiar with Warwick University Clinical Trials Unit's (WCTU) Standard Operating Procedures (SOP) and the University's Research Code of Practice. They have also completed the appropriate online training on IG-Tools hosted by the Health and Social Care Information Centre (HSCIC), which is updated on an annual basis. Each member is also an Approved Researcher with the Office for National Statistics.

To ensure accurate, complete and reliable data, each ambulance service personnale are provided instructional materials that gives instructions for uploading/importing data to, and viewing historical data in, the OHCAO database. An initial training session is also provided for those that will contribute to data entry, which gives instructions on the protocol, and associated procedures. In addition, each AS reporting officer should have undertaken the appropriate IG-Toolkit training.

Automated Audit

In order to provide consistent data validation across the registry, when the ambulance personnel upload data, each OHCAO record is reviewed for completeness and accuracy through an audit algorithm. Adding new content to the registry is completed in two stages, the first uploads the original dataset to be processed by the system and the second imports the cleaned dataset to the registry.

In the first stage, the system reads the mapping instructions to transfer the original source variables to an in-memory data table, substituting the original data item names with the equivalent OHCAO standard. The system then applies the transformation rules in the import rules XML file, and then cleans the transformed data by applying standard data types and coded values. Incompatible values are flagged as “out-of-range” and transformed to NULL (empty). All actions carried out by the system are recorded in the import audit table. The system calculates the import result for every data point to determine if the data is valid, out-of-range or missing. A generic algorithm is used for all data items except date of death, date discharged, time of ROSC and total number of shocks. These data items require specific rules to determine the import result. An overview of the import results is displayed, showing the total number of cases to import and the number of valid, out-of-range and missing values. Aggregated import results for every data item can also be shown. The results for each data point are displayed in either the valid values, out-of-range or missing tabs. The ambulance staff can then either save the data to the registry, or if there are significant errors review the data before then saving it to the registry.

Steering Committee

The Steering Committee provides overall supervision of the project and ensures it is being conducted in accordance with the principles of Good Clinical Practice and the applicable regulations. Day-to-day management of the trial is the responsibility of the Investigators and the Chief Investigator through the Operational Management Group to assist with this function. The Committee comprises of representatives from the funders, the Resuscitation Council (UK) and British Heart Foundation, as well as the co-ordinating centre (University of Warwick), Ambulance Service Medical Directors, representatives of the Chief Executive of Ambulance Services, representative of Ambulance Service Audit Committee, co-applicants, patient/user representatives and other partners. The Chair is chosen by the members from their number.

Quality improvement

We have optimised processes for case ascertainment and outcome verification to reduce variation between the data that is submitted by the different services. We work closely with ambulance services to improve the quality of reported data to the registry and report on this annually.

We collaborated with the International Liaison Committee for Resuscitation to refine international standards to improve consistency of reporting of epidemiology and outcomes from international cardiac arrest registries. One result of this work are Utstein variables, which are standardized variables that ease international comparisons.

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Data Security:

The registry has developed a bespoke, secure web application and database. The web application allows a review of the quality of the data that is submitted by ambulance services. Once reviewed, data is imported to the OHCAO database. The database allows the team to process and report on key system, dispatch, patient, process and outcome variables.

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