A correlation matrix is a table showing correlation coefficients between variables. Each cell in the table shows the correlation between the two variables. A correlation matrix is used to summarize data, as an input into a more advanced analysis, and as a diagnostic for advanced analyses. A correlation matrix is a table showing correlation coefficients between sets of variables. A correlation matrix showing correlation coefficients for combinations of 5 variables B1:B5. The diagonal of the table is always a set of ones because the correlation between a variable and itself is always 1.