CENTRAL creation details
CENTRAL is comprised of a merge of relevant records retrieved from MEDLINE, relevant records retrieved from EMBASE, all Review Groups' Specialised Registers and the handsearch results register, as described below.
Retrieving MEDLINE RCTs and CCTs into CENTRAL
Each quarter, Wiley runs a search strategy against the PubMed version of the MEDLINE database to retrieve new relevant MEDLINE records for CENTRAL. The results of the following search strategy are uploaded into CENTRAL:
#1. randomized controlled trial[PT]
#2. controlled clinical trial[PT]
#3. #1 or #2
#4. limit #3 to human
The Publication Type, or PT, field contains the MEDLINE indexing terms randomized controlled trial, controlled clinical trial or both, as well as other terms describing the publication type (e.g. journal article).
The search strategy above is run each quarter against the entire MEDLINE database starting with the year 1966, and all the retrieved records are uploaded into CENTRAL, replacing the previous set of MEDLINE records in CENTRAL. To reflect changes in health-care practice and to conform with terminology in current use, the MEDLINE thesaurus changes each year, with new terms added and old terms removed. At the beginning of each year, these new MeSH terms are downloaded and added to The Cochrane Library.
A substantial proportion of the records coded randomized controlled trial or controlled clinical trial in the MEDLINE Publication Type field have been so coded as a result of the work of The Cochrane Collaboration. Electronic and handsearch results from Cochrane entities have been sent to the National Library of Medicine, where MEDLINE records have been re-tagged with the publication types RCT and CCT as appropriate. In addition, the US Cochrane Center (USCC) and the UK Cochrane Centre (UKCC) have conducted an electronic search of MEDLINE for randomized and controlled trials using the Cochrane highly sensitive search strategy (Dickersin 1994) for the following years: US Cochrane Center (1966–1984; 1998–2004) and the UK Cochrane Centre (1985–1997). This comprehensive search of MEDLINE 1966–2002 has now been completed and the results have been forwarded to the US National Library of Medicine and re-tagged in MEDLINE. All of the trials identified through this search are also included in each quarterly release of CENTRAL. Pending continued funding, the USCC staff will continue the electronic search of records entered into MEDLINE in 2005 and beyond. Through Wiley's quarterly search and download of all MEDLINE records tagged with the randomized controlled trial or controlled clinical trial Publication Type code, MEDLINE continues to be used as a core building block for the development of CENTRAL.
Retrieving EMBASE RCTs and CCTs into CENTRAL
A retrospective search conducted by the UK Cochrane Centre for reports of trials in EMBASE has been completed for the years 1980 to 2008, for the following free-text terms: random$; factorial$; crossover$; placebo$; doubl$ adj blind$; singl$ adj blind$; assign$; allocat$; volunteer$; and for the following index terms, known as EMTREE terms: crossover-procedure; double-blind procedure; randomized controlled trial; single-blind procedure. A search for the years 1974 to 1979 inclusive has also been completed for the free-text terms: random$; factorial$; crossover$ and placebo$. These searches have yielded a total of approximately 98,000 reports of trials not indexed, at the time of the search, as reports of trials in MEDLINE. All of these reports are now published in CENTRAL.
Specialised Registers
Each of the approximately 50 Review Groups within the Collaboration is responsible for the development of a Specialised Register. The Trials Search Co-ordinators of the Review Groups submit these Specialised Registers in electronic format for processing for CENTRAL. The Review Groups may submit a Specialised Register up to four times a year, corresponding to the four quarterly issues of The Cochrane Library. If a Review Group's register is not submitted for any given quarter, the Group's earlier register submission is published on CENTRAL for that quarterly issue. Each record that has been submitted as part of a specialised register is assigned a specialised register code in CENTRAL. (See Appendix for a list of specialised register codes.)
Handsearch Results
Each of the Cochrane Centres has the responsibility for searching the general healthcare literature of its country or region, and most have now designated one or more staff members to co-ordinate this effort. The Cochrane Review Groups and Fields/Networks are responsible for co-ordinating searching of the specialist literature in their areas of interest. Currently there are approximately 2,400 journals being handsearched. Identified trial reports that are not relevant to a Review Group's scope and thus are not appropriate for their specialised register, and records that are specifically submitted for MEDLINE retagging (see below), are forwarded to Wiley as ‘handsearch results’. These handsearch results must be prepared according to specifications as published in the ‘Guide for Submission of Handsearch Results to CENTRAL’ in the CENTRAL Management Plan. Processing the handsearch results files submitted by Cochrane Groups is a multi-step process that culminates in a single file of handsearch results for publication in CENTRAL. Each record in the handsearch results register is assigned the handsearch code from the Appendix list below, in CENTRAL.
Each quarter, CENTRAL is re-built, using records from the four sources mentioned above, in the following order of precedence: (1) MEDLINE, (2) EMBASE, (3) handsearch results and (4) Specialised Registers. Therefore, for example, if a Specialised Register record matches to an existing MEDLINE or EMBASE record, the MEDLINE or EMBASE source record will be preferentially published. In these cases, the relevant Specialised Register code will be appended to the MEDLINE or EMBASE record in the CENTRAL ‘Cochrane Group Code’ field. No other information from the record, as originally submitted through the Specialised Register, will be added to the corresponding MEDLINE or EMBASE record that is published in CENTRAL.
CENTRAL was created as an immediate repository for all citations to reports of trials identified by the Collaboration. Because of the required quick turn-around time and relative lack of quality control, CENTRAL inevitably contains some typographical errors, duplicates, and reports of non-trials. Thus it is designed primarily for Collaboration use, although as part of The Cochrane Library it is accessible to all users. As resources become available in the future, CENTRAL will be ‘cleaned’ to contain only those reports of studies which are eligible for inclusion in a Cochrane Review.
Reference
Dickersin K, Scherer R, Lefebvre C. 1994. Identifying relevant studies for systematic reviews. BMJ. 309(6964, 12 Nov): 1286–1291 [Full text]
Appendix: Review Group or Field/Network Specialised Register and Handsearch Codes
| SR code | HS code |
Group name |
| SR-ADDICTN | HS-ADDICTN | Drugs and Alcohol Group |
| SR-AIRWAYS | HS-AIRWAYS | Airways Group |
| SR-ANAESTH | HS-ANAESTH | Anaesthesia Group |
| SR-ARI | HS-ARI | Acute Respiratory Infections Group |
| SR-BACK | HS-BACK | Back Group |
| SR-BEHAV | HS-BEHAV | Developmental, Psychosocial and Learning Problems Group |
| SR-BEHAVMED | HS-BEHAVMED | Behavioural Medicines Field |
| SR-BREASTCA | HS-BREASTCA | Breast Cancer Group |
| SR-CANCER | HS-CANCER | Cancer Network |
| SR-CF | HS-CF | Cystic Fibrosis and Genetic Disorders Group |
| SR-CHILD | HS-CHILD | Child Health Field |
| SR-COLOCA | HS-COLOCA | Colorectal Cancer Group |
| SR-COMMUN | HS-COMMUN | Consumers and Communication Group |
| SR-COMPMED | HS-COMPMED | Complementary Medicine Field |
| SR-DEMENTIA | HS-DEMENTIA | Dementia and Cognitive Impairment Group |
| SR-DEPRESSN | HS-DEPRESSN | Depression, Anxiety and Neurosis Group |
| SR-ENDOC | HS-ENDOC | Metabolic and Endocrine Disorders Group |
| SR-ENT | HS-ENT | Ear, Nose and Throat Disorders Group |
| SR-EPILEPSY | HS-EPILEPSY | Epilepsy Group |
| SR-EPOC | HS-EPOC | Effective Practice and Organisation of Care Group |
| SR-EYES | HS-EYES | Eyes and Vision Group |
| SR-FERTILREG | HS-FERTILREG | Fertility Regulation Group |
| SR-GYNAECA | HS-GYNAECA | Gynaecological Cancer Group |
| SR-HAEMATOL | HS-HAEMATOL | Haematological Malignancies Group |
| SR-HIV | HS-HIV | HIV/AIDS Group |
| SR-HTN | HS-HTN | Hypertension Group |
| SR-IBD | HS-IBD | Inflammatory Bowel Disease Group |
| SR-INCONT | HS-INCONT | Incontinence Group |
| SR-INFECTN | HS-INFECTN | Infectious Diseases Group |
| SR-INJ | HS-INJ | Injuries Group |
| SR-LIVER | HS-LIVER | Hepato-Biliary Group |
| SR-LUNGCA | HS-LUNGCA | Lung Cancer Group |
| SR-MENSTR | HS-MENSTR | Menstrual Disorders and Subfertility Group |
| SR-MOVEMENT | HS-MOVEMENT | Movement Disorders Group |
| SR-MS | HS-MS | Multiple Sclerosis Group |
| SR-MUSKEL | HS-MUSKEL | Musculoskeletal Group |
| SR-MUSKINJ | HS-MUSKINJ | Bone, Joint and Muscle Trauma Group |
| SR-NEONATAL | HS-NEONATAL | Neonatal Group |
| SR-NEUROMUSC | HS-NEUROMUSC | Neuromuscular Disease Group |
| SR-ORAL | HS-ORAL | Oral Health Group |
| - | HS-PRECENTRL | Handsearch records lost from CENTRAL before 2000 issue 1 |
| SR-PREG | HS-PREG | Pregnancy and Childbirth Group |
| SR-PROSTATE | HS-PROSTATE | Prostatic Diseases and Urologic Cancers Group |
| SR-PVD | HS-PVD | Peripheral Vascular Diseases Group |
| SR-PUBHLTH also SR-HEALTHP |
HS-PUBHLTH HS-HEALTHP |
Public Health Group |
| SR-REHAB | HS-REHAB | Rehabilitation and Related Therapies Field |
| SR-RENAL | HS-RENAL | Renal Group |
| SR-SCHIZ | HS-SCHIZ | Schizophrenia Group |
| SR-SKIN | HS-SKIN | Skin Group |
| SR-SPECTR | HS-SPECTR | Social, Psychological, and Educational Controlled Trials Register |
| SR-STD | HS-STD | Sexually Transmitted Diseases Group |
| SR-STROKE | HS-STROKE | Stroke Group |
| SR-SYMPT | HS-SYMPT | Pain, Palliation and Supportive Care Group |
| SR-TOBACCO | HS-TOBACCO | Tobacco Addiction Group |
| SR-UPPERGI | HS-UPPERGI | Upper Gastrointestinal and Pancreatic Diseases Group |
| SR-VASC | HS-VASC | Heart Group |
| SR-WOUNDS | HS-WOUNDS | Wounds Group |
Centre Handsearch codes
| HS code | Centre |
|---|---|
| HS-ACC | Australasian Cochrane Centre |
| HS-BCC | Brazilian Cochrane Centre |
| HS-CANCC | Canadian Cochrane Centre |
| HS-CHINESECC | Chinese Cochrane Centre |
| HS-DCC | Dutch Cochrane Centre |
| HS-GCC | German Cochrane Centre |
| HS-IBEROCC | Iberoamerican Cochrane Centre |
| HS-ITALCC | Italian Cochrane Centre |
| HS-NCC | Nordic Cochrane Centre |
| HS-SACC | South African Cochrane Centre |
| HS-SASIANCC | South Asian Cochrane Centre |
| HS-TCN | Thai Cochrane Centre |
| HS-UKCC | UK Cochrane Centre |
| HS-USCC | US Cochrane Centre |
| HS-NBSSI | National Blood Service Systematic Review Initiative |
