Specify coding for covariates for Fit Mixed Effects Model

Stat > ANOVA > Mixed Effects Model > Fit Mixed Effects Model > Coding

Standardize covariates

You can determine whether to standardize the covariates. The standardized covariates are only used to fit the model and are not stored in the worksheet.

Standardizing the covariates can improve the interpretation of the model for specific conditions. You can standardize the covariates using the following methods:
  • Center the covariates by subtracting the mean: This method helps reduce multicollinearity, which improves the precision of the coefficient estimates. This method is helpful when your model contains highly correlated predictors due to higher-order terms and interaction terms. Each coefficient represents the expected change in the response given a one unit change in the predictor, using the original measurement scale.
  • Standardize the covariates by dividing with their corresponding standard deviations. This method allows you to compare the size of the coefficients because they use a comparable scale. This approach is helpful when you want to know which covariates have a larger effect, while controlling for differences in scale. However, each coefficient represents the expected change in the response given a change of one standard deviation in the covariate.
Use one of the following methods to standardize the covariates:
  • Do not standardize: Use your original data for the covariates.
  • Specify low and high levels to code as -1 and +1: Use to both center the covariates and to place them on a comparable scale. All data values that fall between the low and high values that you specify are transformed to fall between −1 and +1. In the table, enter low and high values or use the default minimum and maximum values in the sample.
    Covariate
    Shows the names of all the covariates in your model. This column does not take any input.
    Low
    Enter a value to code as −1. The default is the minimum value in the sample.
    High
    Enter a value to code as +1. The default is the maximum value in the sample.
  • Subtract the mean, then divide by the standard deviation: Use to both center the covariates and to place them on a comparable scale.
  • Subtract the mean: Use to center the covariates.
  • Divide by the standard deviation: Use a comparable scale for all covariates.
  • Subtract a specified value, then divide by another: Specify other values rather than using the mean and standard deviation estimates from the sample.
    Covariate
    Shows the names of all the covariates in your model. This column does not take any input.
    Subtract
    Enter the value to subtract from each covariate.
    Divide By
    Enter the value that Minitab uses to divide the result of the subtraction.
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