You will be shown an excerpt from a computer science scientific research paper, followed by a question about the paper. Please answer the question. Do not include any text in your response other than the answer.

Context: Because the dataset used in this experiment did not have any severe imbalances, the standard deviation was used as a model performance parameter in this study. Because this work deals with multi-class sorting, categorical cross- entropy was chosen as a loss task for all CNN architectures. The activation function employed in all transitional layers of the CNN architectures used in this study was relu, while the last layer's activation function was softmax. The following are the hyperparameters that were used: The dropout rate was 0.3, the learning rate was 0.0001, the batch size was 17, and there were 36 epochs. The model weights were updated using an adaptive moment estimation (Adam) optimizer. Before the resizing, all of the photographs were shrunk to the default image size for each architecture.

Question: How does the author take care of class imbalance problem?
Standard deviation was used as a model performance parameter in this study.