In multivariate statistics, a data matrix is a mathematical matrix of data whose rows represent different repetitions of an experiment, and whose columns represent different types of data (say, the results from particular probes). For example, suppose an experiment is run where 10 people are pulled off the street and asked four questions. The data matrix M would be a 10×4 matrix (meaning 10 rows and 4 columns). The datum in row i and column j of this matrix would be the answer of the i th person to the j th question.
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In linear regression, a design matrix is a data matrix containing explanatory variables.