Data sources and inclusion criteria for the Database on Vitamin A Deficiency
Survey reports and publications reporting the status of vitamin A in populations are collected/requested from:
- Ministries of Health through WHO regional and country offices.
- National research and academic institutions.
- Nongovernmental organizations.
- Organizations of the United Nations system.
- Regular searches of online databases, such as PubMed, Medline, Embase, Ovid, and WHO regional databases (African Index Medicus, Index Medicus for the WHO Eastern Mediterranean Region, Latin American and Caribbean Center on Health Sciences Information, Pan American Health Organization Library Institutional Memory Database, Index Medicus for South-East Asia Region).
These resources are supplemented by manual searching of articles published in non-indexed medical and professional journals and reports from principal investigators.
Data inclusion criteria
Survey data are extracted and included in the database only from original survey reports and publications. Surveys on any administrative level and of any population group are included if they fulfil the following criteria:
- Population-based surveys (exception: facility-based surveys for pregnant women, newborns, preschool-age children, and school-age children, which is strictly mentioned in the ‘General Notes’).
- Cross-sectional surveys.
- Baseline values of intervention studies.
- A clearly defined survey design.
- A minimal sample size of 100 subjects.
- Determination of signs of clinical xerophthalmia and indication of the proportion (%) of the population with one or more of these respective signs AND/OR determination of serum retinol concentrations.
When a potentially relevant survey is identified and the full report obtained, data are checked for consistency as part of routine quality control. If required, data holders are contacted for clarification or to obtain additional results. Available information is extracted and entered into a standard data form. The full archived documentation and correspondence are available on request.