Some analytic tools assess each feature within the context of neighboring features. Feature distances are computed based on the true geometric centroids for each feature. Some features for this dataset have no neighboring features within the given specified distance threshold or when using the specified Conceptualization of Spatial Relationships option.
If you received this warning after running the Cluster and Outlier Analysis tool, the features with no neighbors are reported with NULL values. However, the value of these features were included in the calculation of the mean and other key statistics.
(1) Use a larger distance band threshold, (2) select a Conceptualization of Spatial Relationships value that will ensure each feature has at least one neighbor, or (3) define spatial relationships using the Generate Spatial Weights Matrix tool. Run the tool with a value greater than 0 for the Number of Neighbors parameter.