Sir

Your Technology Feature on micro-array databases and standards, “Share and share alike” (Nature 442, 1069; 2006), is incorrect to state that the National Center for Biotechnology Information's Gene Expression Omnibus (GEO) database is not compliant with MIAME (minimum information about a microarray experiment) standards.

GEO is in fact MIAME-compliant, as it fully supports capture of all data elements defined by MIAME and encourages use of the MIAME checklist in determining what information to submit about an experiment.

Biological context is essential to interpret the underlying data in functional-genomic databases such as GEO. The challenge lies in choosing the right level of detail to require: too little and the database will not be robust enough to meet scientific demands; too much and scientists may be discouraged from submitting, or may inadvertently enter the information inaccurately. The appropriate level of biological context can vary widely between experiments, is difficult to standardize and may change over time. The level of effort a submitter is willing or able to expend may also change with shifting data-submission requirements by journals and funding agencies.

The National Center for Biotechnology Information began GEO in 2000 with a requirement for a minimal level of detail. As the field developed, we encouraged submitters to provide more specific details and modified the database design to include provisions for all MIAME data elements. The result of this incremental approach has been positive, with the growth rate and quality of GEO submissions rising rapidly over time.

Finding and maintaining the optimal balance between complexity and usefulness is challenging, as is providing appropriate tools and resources that evolve with changes in the science and social environment. GEO will continue to monitor the needs of the community and work with the Microarray Gene Expression Data Society and the European Bioinformatics Institute (which produces the ArrayExpress database), as we all seek this balance.