An ML engineer normalized training data by using min-max normalization in AWS Glue DataBrew.

To ensure consistency between training and inference, the min-max normalization statistics (min and max values) calculated during training must be retained and applied to normalize production inference data. Using the same statistics ensures that the model receives data in the same scale and distribution as it did during training, avoiding discrepancies that could degrade model performance. Calculating new statistics from production data would lead to inconsistent normalization and affect predictions.