“…All secondary variables can be merged into a single secondary variable (merged or super‐secondary) using the linear combination (Babak and Deutsch ) provided in the following equation: where the weights are calculated from the system of equations of the multiple linear regression: where , are correlations between secondary data (data redundancy) and are correlations between each secondary variable and the primary variable being predicted; and is the correlation coefficient of the merged/super‐secondary variable with the primary variable being estimated given by the following equation: …”