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Frequently Asked Questions

What is the difference between and submitter-processed datasets?

Samples and the datasets they comprise are designated as if we were able to obtain raw data in a suitable format for one of our processing pipelines. If no suitable raw data is available for a sample on a supported platform, we obtain the processed data available from the source repository and modify it to be more consistent with data; these samples are termed submitter-processed. See the Source Data section for more information.

How do you process the data?

We process samples run on supported microarray platforms with Single-Channel Array Normalization (SCAN) and transcriptomic samples run on supported sequencing platforms with Salmon and tximport. Please see the Processing Information section for more details.

What type of data does support? currently supports gene expression data, specifically genome-scale microarray and RNA-seq data. See our supported microarray and RNA-seq platforms.

What does "corrected" metadata mean?

Scientists will often use different terminology to refer to a similar sample metadata field or key. For example, treatment and treatment protocol may make reference to the same kinds of information. We attempt to perform some mapping between keys to aid in searches. See the Metadata section for more information, including a full list of the mappings we perform.

Why do the values differ a little bit if I download different datasets?

We've prioritized keeping expression values consistent within a dataset based on the samples it contains. Specifically, we remove any genes that are not measured in every sample in a dataset and we do that prior to performing quantile normalization. When using quantile normalization, the expression value a gene is assigned in a particular sample depends on the rank of that gene. If a user download different datasets, which may have different numbers of genes, it's possible then that the same gene in the same sample would have a different expression value between them.

Why do I get a limited number of genes back when I aggregate samples from different platforms?

Different platforms will often measure different sets of genes. These differences can be particularly pronounced when comparing older microarray platforms to more recent platforms. When aggregating samples, we retain only the genes present in every sample. If the dataset delivered to you has fewer genes than you were expecting for that organism, it could be the result of combining multiple platforms or it may be from an older microarray platform.

Why can't I add certain samples to my dataset? will sometimes obtain the metadata (e.g., sample title or experimental protocol) associated with a sample but the raw or submitter processed expression data files are in a format that we can not process. We do not allow you to add these samples to your dataset because we can not deliver expression values.

How can I find out what versions of software/packages were used to process the data?

Version information for the packages we think are most important for data processing is available on the pop-up displayed when you click a sample's processing information link.

The same package information is in the processor list available via our API:

In addition, you may wish to obtain our Docker images (prefixed with dr_) which will allow you to access version information for every dependency.

Are datasets I download batch corrected?

We apply quantile normalization to mitigate issues caused by differences in the underlying distributions of gene expression values in samples. This makes the gene expression values broadly comparable, but doesn't explicitly correct for batch, dataset, or platform. If the scientific question and analysis methods require datasets to be batch corrected, users should first investigate the existence of batch effects using methods such as Principal Components Analysis. If the source dataset is associated with major sources of variability in the data, users may wish to use a meta-analysis framework considering each dataset independently or to apply a batch correction tool. It may be sufficient to include batch, dataset, or platform as covariates for certain analyses.

Why are th�e expression values different if I regenerate a dataset?

The Regenerate Files button triggers the creation of a new dataset using the same options and including the same samples as the original, expired dataset. If there are any changes to the way we process or aggregate datasets (e.g., target quantiles are updated) between the initial dataset creation and regeneration, these will be reflected in the new, regenerated dataset and may result in different values. Users should take this into account when managing datasets obtained from and take steps to appropriately archive datasets they use for analysis.

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