Shipment history for is lumpy

Summary:Shipment history for some items is lumpy and within that if I have to identify outliers and smooth-en the shipment history what should I do?

Content (please ensure you mask any confidential information):

Some of the Items are being bought one in couple of weeks and not consistently. Client also want to identify any outliers (like sudden 100% spike over regular shipments) and smoothen it. I am thinking of creating a custom measure. can I use functions like Avg or stddev in the expression builder?

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):